Dissertations / Theses on the topic 'AlGaN'
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Lundskog, Anders. "Characterization of AlGaN HEMT structures." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9729.
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During the last decade, AlGaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their fundamental electrical properties make them attractive for highpower microwave device applications. Despite much progress, AlGaN HEMTs are far from fully understood and judged by the number of published papers the understanding of advanced structures is even poorer. This work is an exploration of the electrical and structural properties of advanced HEMT structure containing AlN exclusionlayer and double heterojunctions. These small modifications had great impact on the electrical properties.
In this work, AlGaN HEMT structures grown on SiC substrates by a hot-wall MOCVD have been characterized for their properties using optical microscopy, scanning electron microscopy, transmission electron microscopy, capacitance/voltage, eddy-current resistivity, and by homebuilt epi-thickness mapping equipment.
A high electron mobility of 1700 [cm2/Vs] was achieved in an AlN exclusion-layer HEMT. A similar electron mobility of 1650 [cm2/Vs] was achieved in a combination of a double heterojunction and exclusion-layer structure. The samples had approximately the same electron mobility but with a great difference: the exclusion-layer version gave a sheet carrier density of 1.58*1013 [electrons/cm2] while the combination of double heterojunction and exclusion-layer gave 1.07*1013 [electrons/cm2]. A second 2DEG was observed in most structures, but not all, but was not stable with time.
The structures we grew during this work were also simulated using a one-dimensional Poisson-Schrödinger solver and the simulated electron densities were in fairly good agreement with the experimentally obtained. III-nitride materials, the CVD concept, and the onedimensional solver are shortly explained.
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Arehart, Aaron R. "Investigation of electrically active defects in GaN, AlGaN, and AlGaN/GaN high electron mobility transistors." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1253626881.
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Lu, Bin Ph D. Massachusetts Institute of Technology. "AlGaN/GaN-based power semiconductor switches." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82354.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 209-219).
AlGaN/GaN-based high-electron-mobility transistors (HEMTs) have great potential for their use as high efficiency and high speed power semiconductor switches, thanks to their high breakdown electric field, mobility and charge density. The ability to grow these devices on large-diameter Si wafers also reduces device cost and makes them easier for wide market adoption. However, the development of AlGaN/GaN-based power switches has encountered three major obstacles: the limited breakdown voltage of AlGaN/GaN transistors grown on Si substrates; the low performance of normally-off AlGaN/GaN transistors; and the degradation of device performance under high voltage pulsed conditions. This thesis studies these issues and presents new approaches to address these obstacles. The first part of the thesis studies the breakdown mechanism in AlGaN/GaN-on-Si transistors. A new quantitative model-trap-limited space-charge impact-ionization model- is developed. Based on this model, a set of design rules is proposed to improve the breakdown voltage of AlGaN/GaN-on-Si transistors. New technologies have also been demonstrated to increase the breakdown voltage of AlGaN/GaN-on-Si transistors beyond 1500 V. The second part of the thesis presents three technologies to improve the performance of normally-off AlGaN/GaN transistors. First, a dual-gate normally-off MISFET achieved high threshold voltage, high current and high breakdown voltage simultaneously by using an integrated cascode structure. Second, a tri-gate AlGaN/GaN MISFET demonstrated the highest current on/off ratio in normally-off GaN transistors with the enhanced electrostatic control from a tri-gate structure. Finally, a new etch-stop barrier structure is designed to address low channel mobility, high interface density and non-uniformity issues associated with the conventional gate recess technology. Using this new structure, normally-off MISFETs demonstrated high uniformity, steep sub-threshold slope and a record channel effective mobility. The thesis concludes with a new dynamic on-resistance measurement technique. With this method, the hard- and soft-switching characteristics of GaN transistors were measured for the first time.
by Bin Lu.
Ph.D.
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Banerjee, Abhishek. "AlGaN/GaN based enhancement mode MOSHEMTs." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2104/.
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This thesis describes a new gallium nitride (GaN) based transistor technology for electronic switching applications. Conventional GaN based transistors are of the high electron mobility transistor (HEMT) type and are depletion mode devices. These are not suitable for switching applications since an extra DC supply is required to bias the device in the cut-off (off-state) region and the devices are not fail-safe, i.e. incase of malfunction a short-circuit can exist between the main DC supply and ground. Enhancement mode (E-Mode) or normally-off devices can overcome these limitations and if realized in the GaN material system would benefit from the good material properties that support large breakdown voltages and low On-resistances. Fabrication of high performace E-mode GaN devices with low On-resistance and high breakdown voltage still remains a big challenge to date. In this thesis a new method for realizing enhancement mode aluminium gallium nitride - gallium nitride (AlGaN/GaN) devices using a localized gate-foot oxidation has been described. Thermal oxidation of the AlGaN barrier layer converts the top surface/part of this layer into aluminium oxide (Al2 O3 ) and gallium oxide (Ga2O3 ), which serve as a good gate dielectric and improve the gate leakage current by several orders of magnitude compared to a Schottky gate. The oxidation process leaves a thinner AlGaN barrier which can result in normally o§ operation. Without special precaution, however, the oxidation of the AlGaN barrier is not uniform from the top but occurs at higher rates at the defect/dislocation sites. This makes it impossible to control the barrier thickness and so rendering the barrier useless. To avoid the problem of non-uniform oxidation, a thin layer of aluminum is first deposited on the barrier layer and oxidized to form aluminium oxide on top. This additional oxide layer seems to ensure uniform oxidation of the AlGaN barrier layer underneath on subsequent further oxidation. Results of the fabricated 2 um x 100 um AlGaN/GaN MOS-HEMTs with a partially oxidized barrier layer showed a threshold voltage of -0.5 V (compared to -3 V for a Schottky devive fabricated on the same epilayer structure) and a maximum drain current of 800mA/mm at high gate bias of 5 V with very little current compression. The peak extrinsic transconductance of the device is 160 mS/mm at a drain-source voltage of 10 V with a very low specific On-resistance of 9:8 ohm.mm2 and an off-state breakdown voltage higher than 42 V. Capacitance-Voltage (C-V) measurements of Al2O3 /AlGaN /GaN circular test metal-oxide-semiconductor structures were observed and measured. They exhibit no hysteresis, indicating the good quality of the thermally grown aluminium oxide for realizing AlGaN/GaN based E-Mode devices for high frequency and high power applications.
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Schörmann, Jörg. "Cubic AlGaN, GaN structures for device application." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985232277.
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Baltynov, Turar. "Innovative approaches for AlGaN/GaN-based technology." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13522/.
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Gallium Nitride (GaN) has been proven to be a very suitable material for advanced power electronics on account of its outstanding material properties. Today, researchers are exploring GaN-based high electron mobility transistors (HEMTs) for conventional as well as high-end solutions in the range of 600 – 1200 V. However, thermal and power density limitations have impeded the achievement of the peak operational capability of AlGaN/GaN HEMTs. GaN-on-Diamond technology has proven to be a feasible solution to reduce thermal resistance and increase power density of AlGaN/GaN HEMTs for RF applications. The work presented in this thesis is focused on the realisation of high-voltage GaN-on-Diamond power semiconductor devices. This goal was achieved through extensive numerical simulations applied to device design, fabrication, and characterisation. The fabricated devices include conventional AlGaN/GaN HEMT design in circular and linear form with and without field plate engineering. The circular GaN-on-Diamond HEMTs with gate width of ~ 430 μm, gate length of 3 μm, gate-to-drain separation of 17 μm and source field plate length of 3 μm have shown breakdown voltage of ~ 1.1 kV. In this work a new concept of normally-off optically-controlled AlGaN/GaN-based power semiconductor device is proposed. A simulation study has been carried out in order to explore the DC characteristics, switching characteristics, breakdown voltage, and current gain of these novel devices. The typical structure comprises a 20 nm of undoped Al0.23Ga0.77N barrier layer, a 1.1 μm undoped-GaN buffer layer and a p-doped region (to locally deplete the electron channel and ensure a normally-off operation). The simulation study shows that the gain and the breakdown voltage of the device are highly dependent on the depth of the p-doped region. At a particular depth of the p-doped region of 500 nm the gain of the device is 970 (at light intensity of 7 W/cm2) and the breakdown voltage is ~ 350 V. The rise and fall times of the device is found to be 0.4 μsec and 0.3 μsec respectively. The simulation results show a significant potential of the proposed structure for high-frequency and high-power applications.
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Schwarz, Stefan U. [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "Biofunktionalisierung und -sensorik mit AlGaN/GaN-Feldeffekttransistoren." Freiburg : Universität, 2013. http://d-nb.info/1123478864/34.
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Gerrer, Thomas [Verfasser], Oliver [Akademischer Betreuer] Ambacher, and Volker [Akademischer Betreuer] Cimalla. "Transfer von AlGaN/GaN-Hochleistungstransistoren auf Diamant." Freiburg : Universität, 2018. http://d-nb.info/1193052351/34.
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APPASWAMY, ARAVIND C. "SIMULATION OF SHORT CHANNEL AlGaN/GaN HEMTs." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1109277211.
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Phumisithikul, Karen L. "Surface photovoltage transients for p-type AlGaN." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3787.
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There is an understanding of surface photovoltage (SPV) behavior for GaN, yet little is known about the SPV behavior for AlGaN. In this work, a Kelvin probe was used to measure the SPV for p-type AlGaN. Very slow SPV transients were found in AlGaN, which could not be explained with a simple thermionic model. A possible explanation of this behavior is the segregation of impurities to the surface, which causes significant reduction of the depletion region width (down to 2 nm), with carrier tunneling and hopping becoming the dominant mechanisms responsible for the SPV transients. To verify this assumption, the near-surface defective region (about 40 nm) has been removed through the ICP-RIE process. After the etching, the SPV transients became fast and increased in magnitude by about 0.6 eV. By using the thermionic model, band bending was estimated to be -1 eV.
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Kuhn, Bertram. "AlGaN-GaN-Heterostrukturen Epitaxie und elektrische Eigenschaften /." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9755220.
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Ben, Amar Achraf. "Résonateurs MEMS à base d’hétérostructures AlGaN/GaN." Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10073/document.
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En raison de leurs propriétés physiques et leur stabilité chimique, les semi-conducteurs à large bande interdite comme les nitrures d’éléments III doivent permettre de réaliser des dispositifs ayant une meilleure performance dans des environnements sévères. De plus, leur piézoélectricité et la possibilité de les utiliser en technologie monolithique sur silicium rendent cette filière particulièrement intéressante pour intégrer des microsystèmes électro-mécaniques MEMS avec des composants actifs HEMT dans la perspective de réalisation d’une nouvelle génération de capteurs. Le développement des MEMS en matériau nitrures nécessite une bonne connaissance et une bonne maîtrise des propriétés mécaniques des matériaux. La première partie de la thèse consiste donc en la caractérisation des modules d’Young et des contraintes résiduelles dans les couches minces de nitrures épitaxiées par épitaxie par jets moléculaires sur substrat silicium. Pour extraire ces paramètres mécaniques, nous avons mesuré et modélisé des micro-dispositifs de test constitués par des poutres bi-encastrées ou encastrées-libres de longueurs variées et des indicateurs mécaniques. La deuxième partie consiste en l’étude de la transduction électro-mécanique d’actionnement des résonateurs formés par une poutre intégrant une hétérostructure AlGaN/GaN. Les résonateurs sont actionnés par une diode Schottky intégrée sur la poutre. Les actionneurs ont été caractérisés en amplitude et en fréquence de vibration sous différentes conditions de polarisation par vibrométrie laser par effet Doppler. Une modélisation à été effectuée de façon analytique et de façon numérique par éléments finis en utilisant COMSOL multiphysique afin de comprendre le mécanisme d’actionnement et de mettre en évidence le rôle de l’hétérostructure AlGaN/GaN sur le fonctionnement de l’actionneurDue to their physical properties and chemical stability, wide band gap semiconductors such as group III nitrides should enable devices with a better performance in harsh environments. In addition, their piezoelectricity and the possibility of monolithic integration on silicon, make this technology particularly attractive for integrating microelectromechanical systems (MEMS) with active devices such as HEMTs for the purpose of developing a new generation of sensors. The development of MEMS using nitride materials requires a good knowledge and understanding of the mechanical properties of materials. The first part of this thesis concerns the determination of the Young modulus and the residual stress in the thin films of nitrides grown by molecular beam epitaxy on silicon substrate. In order to extract these mechanical parameters, we measured and modelled test devices such as clamped-clamped beams, free-clamped beams with different lengths and mechanical indicators. The second part of the thesis consists in studying the piezoelectric actuation of MEMS resonators based on an AlGaN/GaN heterostructure. The resonators are actuated by a Schottky diode integrated onto the beam. The amplitude of the actuated resonator and the resonant frequency were measured under various bias conditions using Doppler laser vibrometry. We performed analytical modelling and finite element modelling using COMSOL Multiphysics® in order to unerstand the actuation mechanism and to evidence the role of the AlGaN/GaN heterostructure on the actuator operation
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Greco, Giuseppe. "AlGaN/GaN heterostructures for enhancement mode transistors." Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1347.
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Today the continuous increase of electric power demand is in our society a global concern. Hence, the reduction of the energy consumption has become the main task of modern power electronics. In this context, wide band semiconductors (WBG), such as gallium nitride (GaN) and related alloys, have outstanding physical properties that can enable to overcome the limitations of Silicon, in terms of operating power, frequency and temperature of the devices.
An interesting aspects related to GaN materials is the possibility to grow AlGaN/GaN heterostructures, in which a two dimensional electron gas (2DEG) is formed at the heterojunction. Basing on the presence of the 2DEG, AlGaN/GaN heterostructures are particularly interesting for the fabrication of high electron mobility transistors (HEMTs).
One of the most challenging aspects on this field is the development of enhancement mode AlGan/GaN HEMT. This devices would offer a simplified circuitry, in combination with favourable operating conditions for device safety. Hence, this thesis is entitled AlGaN/GaN heterostructures for enhancement mode transistors .
The aim of this work was to clarify the mechanisms ruling the electronic transport at some relevant interfaces in AlGaN/GaN devices, after surface modification processes used in normally-off technologies.
The thesis is divided in 6 chapters. In the first two chapters, the properties of GaN and related AlGaN alloys are described, explaining the formation of the 2DEG and the working principle of HEMT devices.
In chapter 3, a nanoscale characterization of modified AlGaN surfaces is presented in order to deplete the 2DEG. Two different approaches have been studied, i.e., the use of a fluorine plasma treatment and the use of a local oxidation process. Even though a depletion of the 2DEG is possible, several reliability concerns need to be investigated before a practical application to devices can be envisaged.
Among the possible approaches for enhancement mode transistors using AlGaN/GaN heterostructures, the use of a p-GaN gate contact seems to be the most interesting one. Hence, chapter 4 reports a detailed investigation on the formation of Ohmic contact to p-GaN. The evolution of a Au/Ni bilayer, annealed at different temperatures and in two different atmospheres (Ar or N2/O2) was considered. The electrical measurements of the contacts annealed under different conditions demonstrated a reduction of the specific contact resistance in oxidizing atmosphere. Structural characterizations of the metal layer associated with nanoscale electrical measurements, allowed to give a possible scenario on the Ohmic contact formation mechanisms. Finally, the temperature dependence of the specific contact resistance allowed the extraction of the metal/p-GaN barrier.
The fabrication and characterization of AlGaN/GaN transistors with the use of a p-GaN cap layer under the gate contact is presented in chapter 5.
The electrical characterization of p-GaN/AlGaN/GaN transistors demonstrated a significant positive shift of the threshold voltage (Vth) with respect to devices without p-GaN gate. A normally-off behaviour of the devices (Vth= +1.4 V) was obtained upon a reduction of the barrier layer thickness and Al concentration.
Finally, a preliminary study on the use of nickel oxide (NiO) as a dielectric below the Schottky gate contact in AlGaN/GaN heterostructures is reported in the last chapter. First, a structural and morphological investigation of the NiO layers grown by MOCVD showed continuous epitaxial film. The electrical measurements on devices allowed to extract a value of the dielectric constant for the grown NiO very close to the theoretical one, and a reduction of the leakage current in HEMT structures integrating such a dielectric.
The experimental results of this thesis are summarized in the conclusive section, that also briefly describes the remaining open issues and the possible continuation of this research activity.
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Bradley, Shawn Todd. "Investigation of AlGaN films and nickel/AlGaN Schottky diodes using depth-dependent cathodoluminescence spectroscopy and secondary ion mass spectrometry." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078329692.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxii, 182 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Leonard J. Brillson, Dept. of Electrical Engineering. Includes bibliographical references (p. 173-182).
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Krauße, Daniel [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "High power AlGaN/GaN HFETs for industrial, scientific and medical applications = AlGaN/GaN Hochleistungstransistoren für industrielle, wissenschaftliche und medizinische Anwendungen." Freiburg : Universität, 2013. http://d-nb.info/112347737X/34.
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Seifert, Oliver. "Persistente Photoleitfähigkeit in dünnen GaN- und AlGaN-Schichten." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=958338477.
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Haratizadeh, Hamid. "Optical characterization of GaN/AlGaN quantum well structures /." Linköping : Univ, 2004. http://www.bibl.liu.se/liupubl/disp/disp2004/tek866s.pdf.
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Linkohr, Stefanie [Verfasser], and Oliver [Akademischer Betreuer] Ambacher. "AlGaN/GaN-basierte-pH-Sensoren für biochemische Anwendungen." Freiburg : Universität, 2011. http://d-nb.info/1123465223/34.
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Ngoepe, P. N. M. (Phuti Ngako Mahloka). "Optoelectronic characterisation of AlGaN based Schottky barrier diodes." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/24890.
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Recent advances in growth techniques have lead to the production of high quality GaN and this has played a vital role in the improvement of GaN based devices. A number of device types can be produced from GaN. Spectrally selective devices can be produced by creating ternary or quaternary material systems by partially substituting either Al or In for Ga in GaN. This allows a wide spectral range that can be achieved ranging from the visible to the ultraviolet. The applications of detectors based on these material systems are vast and include areas such as biological, military, environmental, industrial and scientific spheres. In front illuminated Schottky barrier photodetectors, two major factors influencing the sensitivity of the device are the reverse leakage current and the transparency of the Schottky contact. In order to reduce the reverse current of semiconductor based devices, increase the barrier height, and enhance the adhesion of a metal on a semiconductor it is important to subject the contact to annealing. Annealing studies have been performed on AlGaN based photodiodes to investigate the evolution of the optical and electrical properties. In this study, the electrical and optical characteristics of AlGaN based Ni/Au and Ni/Ir/Au Schottky photodiodes were investigated. The electrical properties of the photodiodes were optimised by annealing in an Ar ambient. An increase in the Schottky barrier height and a decrease in the reverse leakage current were observed with increasing annealing temperature up to 500 oC. This effect was observed for both the Ni/Au and Ni/Ir/Au photodiodes. The optical characteristics of the photodiodes, which include the responsivity and the quantum efficiency, were also investigated. UV/visible rejection ratios of as high as 103 were obtained. The transmittance of Ni/Au and Ni/Ir/Au metal layers deposited on a quartz substrate were optimised by annealing. This was under the same ambient conditions as the Schottky photodiode. The transmittance increased with annealing temperature for the Ni/Au metal layer whereas it decreased at higher temperatures for the Ni/Ir/Au layer. The transmittance of the Ni/Au metal layer reached as high as 85 % after 500 oC annealing. The transmittance of the Ni/Ir/Au only reached a high of 41 % after 400 oC annealing.Dissertation (MSc)--University of Pretoria, 2013.
Physics
unrestricted
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Bajaj, Sanyam. "Design and Engineering of AlGaN Channel-Based Transistors." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1514904566666781.
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Spisser, Hélène. "Développement de capteurs THz utilisant l'hétérostructure AlGaN/GaN." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/10290.
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Le domaine du spectre électromagnétique correspondant aux fréquences térahertz est encore peu exploité, pourtant, les applications nécessitant la génération, l’amplification ou la détection d’un signal térahertz sont nombreuses et intéressantes. Dans ce travail, nous nous intéressons tout particulièrement au détecteurs plasmoniques, qui constituent une alternative prometteuse à la montée en fréquence des capteurs électroniques et à l’utilisation de capteurs thermiques pour les photons de faible énergie.
Les capteurs plasmoniques fonctionnent grâce au couplage entre le photon térahertz et un plasmon au sein d’un gaz d’électrons bidimensionnel (2DEG). Le plasmon-polariton est ensuite transformé en un signal continu et détectable. Nous utilisons pour cela le 2DEG présent dans l’hétérostructure AlGaN/GaN. Le couplage entre le photon et le plasmon-polariton est réalisé par un réseau métallique déposé sur la structure semi-conductrice.
Tout d’abord, l’étude du couplage photon/plasmon par des simulations électromagnétiques nous a permis de connaître les fréquences de résonance des plasmons-polaritons en fonction des dimensions du réseau. Le motif de réseau composé de deux bandes de métal de largeurs différentes a été plus particulièrement étudié. Ce motif permettant aux détecteurs d’atteindre une très haute sensibilité [Coquillat et al., 2010] et n’avait pas encore été étudié du point de vue de son efficacité de couplage.
Des détecteurs, dimensionnés pour notre montage de test à 0,65 THz, ont ensuite été fabriqués puis mesurés avec un réseau non-polarisé, à température ambiante et refroidis à l’azote. La correspondance entre la variation de la sensibilité en fonction de la fréquence et les spectres d’absorption mesurés au spectromètre infrarouge à transformée de Fourier (FTIR) montre l’importance de l’étape de couplage dans le processus de détection.
Contrôler la densité électronique dans le 2DEG permet de modifier la fréquence de résonance des plasmons-polaritons et d’augmenter la sensibilité des détecteurs. Nous avons mené des développements technologiques de manière à pouvoir contrôler la densité électronique du 2DEG en appliquant une tension sur le réseau. Cette étape constitue un défi technologique compte tenu de la surface très étendue des réseaux (plusieurs mm²). Nous avons finalement fabriqué des détecteurs pour lesquels la fréquence de résonance de couplage peut être contrôlée grâce à la tension appliquée sur le réseau.Abstract: The objectives of this thesis were the fabrication, the measurement and the study of gallium nitride THz detectors. These detectors are working as follows : first the incident THz photon is coupled to a plasmon in the quantum well at the interface AlGaN/GaN. This plasmon is then turned into a continuous measurable current. One of the key-components in this type of detectors is the grating coupling the incident photon and the plasmon. Electromagnetic simulations have been made to determine the dimensions of the grating depending on the detection frequency. Detectors were then fabricated using the precendently calculated grating patterns. Their working frequency depending on their dimensions were measured with a good agreement with the previously led simulations. The grating is not used only as coupling element, but can be used to monitor the electron density in the quatum well as well, what should allow an exaltation of the rectification phenomenon and a frequency tunability. A technological development was needed to achieve grating actually monitoring the electron density over a wide range. It was a real challenge to fabricate such wide grating (36 mm²) with such small periods (about one micrometer) using epitaxies developped for devices with a much smaller area.
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Ajay, Akhil. "Nanofils de GaN/AlGaN pour les composants quantiques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY030/document.
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Ce travail se concentre sur l'ingénierie Intersubband (ISB) des nanofils où nous avons conçu des hétérostructures de GaN / (Al, Ga) N intégrées dans un nanofil GaN pour le rendre optiquement actif dans la région spectrale infrarouge (IR), en utilisant un faisceau moléculaire assisté par plasma épitaxie comme méthode de synthèse. Les transitions ISB se réfèrent aux transitions d'énergie entre les niveaux confinés quantiques dans la bande de conduction de la nanostructure.Un contrôle précis des niveaux élevés de dopage est crucial pour les dispositifs ISB. Par conséquent, nous explorons Ge comme un dopant alternatif pour GaN et AlGaN, pour remplacer le Si couramment utilisé. Nous avons cultivé des couches minces de GaN dopé Ge avec des concentrations de porteurs atteignant 6,7 × 1020 cm-3 à 300 K, bien au-delà de la densité de Mott, et nous avons obtenu des couches minces conductrices AlxGa1-xN dopées Ge avec une fraction molaire Al jusqu'à x = 0,64. Dans le cas de GaN, la présence de Ge n'affecte pas la cinétique de croissance ou les propriétés structurales des échantillons. Cependant, dans des échantillons AlxGa1-xN dopés par Ge avec x> 0,4, la formation de grappes riches en Ge a été observée, avec une baisse de la concentration du porteur.Ensuite, nous avons réalisé une étude comparative du dopage Si vs Ge dans des hétérostructures GaN / AlN pour des dispositifs ISB dans la gamme IR à courte longueur d'onde. Nous considérons les architectures planaire et nanofils avec des niveaux de dopage et des dimensions de puits identiques. Sur la base de cette étude, nous pouvons conclure que les deux Si et Ge sont des dopants appropriés pour la fabrication d'hétérostructures GaN / AlN pour l'étude des phénomènes optoélectroniques ISB, à la fois dans les hétérostructures planaires et nanofils. Dans cette étude, nous rapportons la première observation de l'absorption d'ISB dans des puits quantiques GaN / AlN dopés au Ge et dans des hétérostructures de nanofils GaN / AlN dopés au Si. Dans le cas des nanofils, nous avons obtenu une largeur de ligne d'absorption ISB record de l'ordre de 200 meV. Cependant, cette valeur est encore plus grande que celle observée dans les structures planaires, en raison des inhomogénéités associées au processus de croissance auto-assemblé.En essayant de réduire les inhomogénéités tout en gardant les avantages de la géométrie des nanofils, nous présentons également une analyse systématique de l'absorption de l'ISB dans les micro et nanopillars résultant d'un traitement top-down des hétérostructures planaires GaN / AlN. Nous montrons que lorsque l'espacement du réseau de piliers est comparable aux longueurs d'onde sondées, les résonances des cristaux photoniques dominent les spectres d'absorption. Cependant, lorsque ces résonances sont à des longueurs d'onde beaucoup plus courtes que l'absorption ISB, l'absorption est clairement observée, sans aucune dégradation de son amplitude ou de sa largeur de raie.Nous explorons également la possibilité d'étendre cette technologie de nanofils à des longueurs d'onde plus longues, pour les absorber dans la région IR à mi-longueur d'onde. En utilisant des hétérostructures de nanofils GaN / AlN, nous avons fait varier la largeur du puits GaN de 1,5 à 5,7 nm, ce qui a conduit à un décalage rouge de l'absorption ISB de 1,4 à 3,4 μm. Remplaçant les barrières AlN par Al0.4Ga0.6N, le composé ternaire représente une réduction de la polarisation, ce qui conduit à un nouveau décalage rouge des transitions ISB à 4,5-6,4 um.L'observation de l'absorption de l'ISB dans des ensembles de nanofils nous a motivés pour le développement d'un photodétecteur infrarouge à puits quantiques à base de nanofils. La première démonstration d'un tel dispositif, incorporant une hétérostructure de nanofils GaN / AlN qui absorbe à 1,55 μm, est présentée dans ce manuscritDue to its novel properties nanowires have emerged as promising building blocks for various advanced device applications. This work focuses on Intersubband (ISB) engineering of nanowires where we custom design GaN/(Al,Ga)N heterostructures to be inserted in a GaN nanowire to render it optically active in the infrared (IR) spectral region. ISB transitions refer to energy transitions between quantum confined levels in the conduction band of the nanostructure. All the structures analised in this thesis were synthesized by plasma-assisted molecular beam epitaxy.Precise control of high doping levels is crucial for ISB devices. Therefore, we explored Ge as an alternative dopant for GaN and AlGaN, to replace commonly-used Si. We grew Ge-doped GaN thin films with carrier concentrations of up to 6.7 × 1020 cm−3 at 300 K, well beyond the Mott density, and we obtained conductive Ge-doped AlxGa1-xN thin films with an Al mole fraction up to x = 0.66. In the case of GaN, the presence of Ge does not affect the growth kinetics or structural properties of the samples. However, in Ge doped AlxGa1-xN samples with x > 0.4 the formation of Ge rich clusters was observed, together with a drop in the carrier concentration.Then, we performed a comparative study of Si vs. Ge doping in GaN/AlN heterostructures for ISB devices in the short-wavelength IR range. We considered both planar and nanowire architectures with identical doping levels and well dimensions. Based on this study, we concluded that both Si and Ge are suitable dopants for the fabrication of GaN/AlN heterostructures for the study of ISB optoelectronic phenomena, both in planar and nanowire heterostructures. Within this study, we reported the first observation of ISB absorption in Ge-doped GaN/AlN quantum wells and in Si-doped GaN/AlN nanowire heterostructures. In the case of nanowires, we obtained a record ISB absorption linewidth in the order of 200 meV. However, this value is still larger than that observed in planar structures, due to the inhomogeneities associated to the self-assembled growth process.Trying to reduce the inhomogeneities while keeping the advantages of the nanowire geometry, we also presented a systematic analysis of ISB absorption in micro- and nanopillars resulting from top-down processing GaN/AlN planar heterostructures. We showed that, when the spacing of the pillar array is comparable to the probed wavelengths, photonic crystal resonances dominate the absorption spectra. However, when these resonances are at much shorter wavelengths than the ISB absorption, the absorption is clearly observed, without any degradation of its magnitude or linewidth.We also explore the possibility to extend this nanowire technology towards longer wavelengths, to absorb in the mid-wavelength IR region. Using GaN/AlN nanowire heterostructures, we varied the GaN well width from 1.5 to 5.7 nm, which led to a red shift of the ISB absorption from 1.4 to 3.4 µm. Replacing the AlN barriers by Al0.4Ga0.6N, the reduction of polarization led to a further red shift of the ISB transitions to 4.5-6.4 µm.The observation of ISB absorption in nanowire ensembles motivated us for the development of a nanowire-based quantum well infrared photodetector (NW-QWIP). The first demonstration of such a device, incorporating a GaN/AlN nanowire heterostructure that absorbs at 1.55 µm, is presented in this manuscript
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Fontserè, Recuenco Abel. "Advanced AlGaN/GaN HEMT technology, design, fabrication and characterization." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/129098.
Full textAbstract:
Nowadays, the microelectronics technology is based on the mature and very well established silicon (Si) technology. However, Si exhibits some important limitations regarding its voltage blocking capability, operation temperature and switching frequency. In this sense, Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) devices have the potential to make this change possible. The unique combination of the high-breakdown field, the high-channel electron mobility of the two dimensional electron gas (2DEG), and high-temperature of operation has attracted enormous interest from social, academia and industry and in this context this PhD dissertation has been made. This thesis has focused on improving the device performance through the advanced design, fabrication and characterization of AlGaN/GaN HEMTs, primarily grown on Si templates.
The first milestone of this PhD dissertation has been the establishment of a know-how on GaN HEMT technology from several points of view: the device design, the device modeling, the process fabrication and the advanced characterization primarily using devices fabricated at Centre de Recherche sur l'Hétéro-Epitaxie (CRHEA-CNRS) (France) in the framework of a collaborative project. In this project, the main workhorse of this dissertation was the explorative analysis performed on the AlGaN/GaN HEMTs by innovative electrical and physical characterization methods. A relevant objective of this thesis was also to merge the nanotechnology approach with the conventional characterization techniques at the device scale to understand the device performance.
A number of physical characterization techniques have been imaginatively used during this PhD determine the main physical parameters of our devices such as the morphology, the composition, the threading dislocations density, the nanoscale conductive pattern and others. The conductive atomic force microscopy (CAFM) tool have been widely described and used to understand the conduction mechanisms through the AlGaN/GaN Ohmic contact by performing simultaneously topography and electrical conductivity measurements. As it occurs with the most of the electronic switches, the gate stack is maybe the critical part of the device in terms of performance and longtime reliability. For this reason, how the AlGaN/GaN HEMT gate contact affects the overall HEMT behaviour by means of advanced characterization and modeling has been intensively investigated.
It is worth mentioning that the high-temperature characterization is also a cornerstone of this PhD. It has been reported the elevated temperature impact on the forward and the reverse leakage currents for analogous Schottky gate HEMTs grown on different substrates: Si, sapphire and free-standing GaN (FS-GaN). The HEMT' forward-current temperature coefficients (T^a) as well as the thermal activation energies have been determined in the range of 25-300 ºC. Besides, the impact of the elevated temperature on the Ohmic and gate contacts has also been investigated.
The main results of the gold-free AlGaN/GaN HEMTs high-voltage devices fabricated with a 4 inch Si CMOS compatible technology at the clean room of the CNM in the framework of the industrial contract with ON semiconductor were presented. We have shown that the fabricated devices are in the state-of-the-art (gold-free Ohmic and Schottky contacts) taking into account their power device figure-of-merit ((VB^2)/Ron) of 4.05×10^8 W/cm^2. Basically, two different families of AlGaN/GaN-on-Si MIS-HEMTs devices were fabricated on commercial 4 inch wafers: (i) using a thin ALD HfO2 (deposited on the CNM clean room) and (ii) thin in-situ grown Si3N4, as a gate insulator (grown by the vendor). The scientific impact of this PhD in terms of science indicators is of 17 journal papers (8 as first author) and 10 contributions at international conferences.
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Potthast, Stefan. "Growth and characterization of cubic AlGaN/GaN based devices." [S.l.] : [s.n.], 2006. http://ubdata.uni-paderborn.de/ediss/06/2007/potthast.
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Zeisel, Roland. "Optoelectronic properties of defects in diamond and AlGaN alloys." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962138452.
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Wu, Yichao. "RF circuit applications of enhancement-mode AlGaN/GaN HEMTs /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20WUY.
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Cherns, Peter David. "A transmission electron microscopy study of AlGaN/GaN heterostructures." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597581.
Full textAbstract:
The use of an A1N interlayer to allow the growth of crack-free AlGaN on a GaN template is investigated. The impact of using an A1N interlayer on the active region of a device is examined by investigating a series of GaN/AlGaN quantum well structures. It is observed by WBDF that the a-type dislocations generated at the A1N interlayer form ‘staircase’ structures in the quantum well stack where all dislocation segments are in edge orientation A model is proposed where misfit dislocation segments at each well interface are formed by climb, in contrast to the dislocation glide at the lowest interface that might be expected in other systems. Both HAADF imaging and conventional TEM are used to characterise a series of Al-GaN/GaN quantum cascade laser (QCL) structures. These devices have great potential in the field of fibre optic communication. Changes in the layer spacing near V-defects, and the effects that changing substrate from sapphire to bulk GaN have on the mechanisms for relaxation in this system are identified and discussed.
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Nilsson, Daniel. "Doping of high-Al-content AlGaN grown by MOCVD." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-106733.
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The high-Al-content AlxGa1-xN, x > 0.70, is the principal wide-band-gap alloy system to enable the development of light-emitting diodes operating at the short wavelengths in the deep-ultraviolet, λ < 280 nm. The development of the deep-ultraviolet light-emitting diodes (DUV LEDs) is driven by the social and market impact expected from their implementation in portable units for water disinfection and based on the damaging effect of the deep-ultraviolet radiation on the DNA of various microorganisms. Internationally, intense research and technology developments occur in the past few years, yet, the external quantum efficiency of the DUV LEDs is typically below 1%. One of the main material issues in the development of the DUV LEDs is the achievement of n- and ptype doped layers of high-Al-content AlxGa1-xN with low resistivity, which is required for the electrical pumping of the diodes. The doping process, however, becomes significantly more complex with increasing the Al content and the resistivity value can be as high as 101-102 Ω cm for n-type AlN doped by silicon, and 107-108 Ω cm for p-type AlN doped by magnesium. The present study is therefore focused on gaining a better understanding of the constraints in the doping process of the high-Al-content AlxGa1-xN alloys, involving mainly the silicon dopant. For this purpose, the epitaxial growth of the high-Al-content AlxGa1-xN and AlN by the implementation of the distinct hot-wall MOCVD is developed in order to achieve layers of good structural and morphological properties, and with low content of residual impurities, particularly oxygen and carbon. Substitutional point defects such as ON and CN may have a profound impact on the doping by their involvement in effects of n-type carrier compensation. The process temperature can be set from 1000 °C and up to 1400 °C in the present study, which is a principal advantage in order to optimize the material properties of the high-Al-content AlxGa1-xN and AlN. The epitaxial growth of the high-Alcontent AlxGa1-xN and AlN is largely performed on 4H-SiC substrates motivated by (i) the lattice mismatch of ~ 1% along the basal plane (the smallest among other available substrates including Si and sapphire), (ii) the good thermal conductivity of 3.7 W cm-1 K-1, which is essential to minimize the self-heating during the operation of any light-emitting diode, and (iii) the limited access to true-bulk AlN wafers. The Si doping is investigated over a large range of [Si] ~ 1×1017 cm-3 - 1×1020 cm-3. Only the high doping range of [Mg] ~ (1-3)×1019 cm-3 is targeted motivated by the large thermal ionization energy of this common acceptor (from 200 meV in GaN to about 630 meV in AlN). The material characterization involves extensive implementation of atomic force microscopy (AFM), x-ray diffraction (XRD), cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), capacitancevoltage measurements, as well as measurements of the conductivity of the layers by contactless microwave-based technique. The possibility to perform electron paramagnetic resonance (EPR) measurements on the Si-doped high-Al-content AlxGa1-xN is essential in order to establish any effect of self-compensation of the shallow donor state of silicon through the related so-called DX state. The EPR measurements corroborate the study of the incorporation kinetics of silicon and oxygen at various process temperatures and growth rates. The outcome of this study is accordingly summarized and presents our understanding for (i) the complex impact of silicon and oxygen on the n-type conductivity of Al0.77Ga0.23N, which is the alloy composition at which a drastic reduction of the n-type conductivity of high-Al-content AlxGa1-xN is commonly reported (paper 1); (ii) the strain and morphology compliance during the intentional doping by silicon and magnesium, and its correlation with the resistivity in the highly doped layers of Al0.82Ga0.18N alloy composition (paper2); (iii) the n-type conductivity of highly-Si-doped Al0.72Ga0.28N layers as bound by the process temperature (paper 3); and (iv) the shallow donor or DX behavior of the Si dopant in conductive AlxGa1-xN layers, 0.63 ≤ x ≤ 1 (paper 4). It is noted that the measured n-type conductivity in reference layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition is on par with the state-of-the-art values, i.e. ≤ 0.05 Ω cm, and 0.012 Ω cm, respectively. A room-temperature resistivity of 7 kΩ cm is measured in Mg-doped layers of Al0.85Ga0.15N alloy composition, which is superior to the state-of-art values (paper 5). The performance of the transport properties of the high-Al-content AlxGa1-xN layers is expected to improve with improvement of their material quality. This can be achieved by improvement of the crystalline quality of the AlN-on-SiC template and by the implementation of true-bulk AlN substrates. The AlN heteroepitaxial growth at the process temperatures of 1100-1200 °C is therefore investigated (paper 6). The lattice constants, structural and optical properties of true-bulk, homoepitaxial and heteroepitaxial AlN material grown at high process temperatures of up to 1400 °C is further reported (paper 7).
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Saadat, Omair I. "Processing technology for high quality AlGaN/GaN MOSHEMT interfaces." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97810.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 120-126).
Gallium Nitride (GaN) based high electron mobility transistors (HEMTs) are very promising for applications requiring high power and high operating frequencies due to its intrinsic material properties like the high electron mobility, large critical electric field and large carrier concentration. For power switching applications, it is necessary to lower gate leakage by introducing a gate insulator between the gate metal and the AIGaN barrier. This thesis focuses on studying the impact of processing conditions on the quality of the gate stack of AIGaN/GaN based MISHEMTs. First, the role of mobile ions like sodium in impacting the threshold voltage of AIGaN/GaN MIS-HEMTs was studied. Characterization techniques like bias temperature stress (BTS) that were traditionally used for characterizing mobile ions in SiO₂/Si capacitors were adapted for AIGaN/GaN MISHEMTs. Next, the impact of fabricating Al₂O₃/AIGaN/GaN MISHEMTs by using a CMOS compatible gate first process flow vs an Au-contact based, liftoff oriented process flow was evaluated. The differences between capacitors and transistors fabricated by different process flows were evaluated by a combination of high bias capacitance-voltage (CV) and transient current-voltage (IV) measurements. Organic contamination from the ohmic first process flow was attributed as being the key cause of the superior interface for the AIGaN/GaN MISHEMT processed using a gate first process flow. Finally, the gate first process flow was used to fabricate additional AIGaN/GaN MISHEMTS in order to look at the impact of atomic layer deposition (ALD) nucleation layers, the AIN interlayer, annealing conditions and AIGaN oxidation on the quality of the gate stack.
by Omair I. Saadat.
Ph. D.
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Malik, Adil Mahmood. "Technology and physics of gate recessed GaN AlGaN FETs." [S.l. : s.n.], 2003. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-30157.
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Nguyen, Quan H. "Physical Sensing Effects in AlGaN/GaN Heterostructure and Applications." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/411259.
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Gallium nitride (GaN) is a promising material for electronic sensing devices operating in harsh environments, thanks to its large energy band gap, superior mechanical properties and excellent chemical inertness. Among various wide energy band gap semiconductors such as 3C-SiC, 4H-SiC, 6H-SiC materials, GaN and its compounds are considered as the most suitable materials for Micro Electro-Mechanical Systems (MEMS) sensors for harsh environment applications, as it can be grown on both sapphire and Si substrates, which are compatible with conventional MEMS fabrication processes, while reducing the cost of GaN wafers. GaN-based electronic devices for high frequency and high power applications have been already commercially available. However, their application in sensing is still underdeveloped and under-commercialized.
This research aims to experimentally investigate and theoretically analyze the physical sensing effects, such as piezotronic, Hall, pseudo-Hall, and phototronic effects on Al-GaN/GaN heterojunctions, and explores the potential of enhancing the sensitivity of AlGaN/GaN-based sensing devices through multi-physics coupling effect.
The first purpose of this study is to examine the effect of external strain on the polarization and electronic properties of the p-GaN/AlGaN/GaN heterostructure (piezotronic effect) and evaluates the possibility to utilize the effect as a strain sensing mechanism. Theoretical analysis on the strain induced effect in the energy band structure is thoroughly conducted. p-GaN/AlGaN/GaN based sensing devices are fabricated and characterized, which exhibit high sensitivity, excellent linearity, and good repeatability, indicating the potential for pressure/strain sensing. In addition, the possibility of enhancing the sensitivity of an p-GaN/AlGaN/GaN heterostructure based piezotronic sensor by employing the photoexcitation-electronic coupling effect is also investigated. The research analyses the key parameters contributing to this tuneable giant piezotronic effect and figures out the physical mechanism leading to this phenomenon.
The next goal is to characterize the performance of the AlGaN/GaN-based current sensor and AlGaN/GaN van der Pauw strain sensor utilizing Hall and pseudo-Hall effects, respectively. Both current sensor and van der Pauw sensor exhibit high sensitivity, excellent repeatability and linearity, while the current sensor operates at a temperature range from room to 200 degrees C with negligible changes in sensitivity. Combining these performances with the excellent mechanical strength, electrical conductivity, and chemical inertness of GaN, the proposed sensors are promising for strain and power monitoring in harsh environments.
Furthermore, this research also intends to investigate the phototronic behaviors of the AlGaN/GaN heterojunction under UV illuminations (phototronic e ect). The characteristics of the heterojunction are also evaluated under broad spectral illuminations to prove its potential for high-performance visible-blind UV light detector. Moreover, the in-depth discussion about the carrier generation and transport mechanisms will provide vital information for the development of AlGaN/GaN optoelectronic sensing devices. This thesis is prepared in a \thesis by publications" format. The published and submitted journal articles are the main contents of chapters 3, 4, 5, and 6.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Kuo, Che-Fu, and 郭哲輔. "AlGaN-Based Photodetectors." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/16933157738923975890.
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碩士國立成功大學
微電子工程研究所碩博士班
95
In this thesis, LT-GaN layer with different thickness (i.e. 15, 30 and 60 nm) were first deposited on top of AlGaN/GaN heterostructure. AlGaN/GaN Schottky barrier photodetectors with these LT-GaN cap layers were then fabricated. It was found that the reverse dark currents were all around 2 × 10 – 10 A of these three samples at - 10 V bias. This value is much smaller than those of Schottky-barrier photodetectors without LT-GaN cap layer. It indicates that dark currents were reduced and Schottky barrier heights were enhanced by utilizing LT-GaN cap layers. With an incident light wavelength of 320 nm, it was found that measured peak responsivities under - 1 V bias were 0.053, 0.044 and 0.031 A/W, corresponding to quantum efficiencies of 20.4%, 17.2% and 12.1% for the photodetectors with 15, 30 and 60-nm-thick LT-GaN cap layers, respectively. On the other hand, with a - 1 V applied bias, the Schottky-barrier photodetector with 15-nm-thick LT-GaN cap layer also exhibits the minimum NEP of 4.88 × 10-13 W and the maximum D* of 8.19 × 1012 cmHz0.5W-1 among these Schottky PDs. For the second part, the similar structure was employed for UV-B bandpass photodetectors. Al0.2Ga0.8N/GaN Schottky-barrier PDs with ITO Schottky contacts on 15-nm-thick LT-GaN cap layers were fabricated and characterized. It was found that the transmittance of ITO films decreases rapidly in the short wavelength region showing a step absorption edge. In addition, the absorption edge of ITO films red-shifted as the films annealed or with increased thicknesses. The response spectra of our bandpass photodetectors were judged by absorption profiles of ITO films significantly. In other words, UV-B PDs could be realized with different bandwidths by controlling thicknesses and annealing conditions. Under - 1 V bias, the photodetectors with 70-nm-thick ITO contact showed the peak responsivity and the peak external quantum efficiency of 0.107 A/W and 41.56% respectively. On the other hand, it also exhibited the minimum NEP of 2.21 × 10-13 W and the maximum D* of 1.81 × 1013 cmHz0.5W-1, among these bandpass photodetectors. Finally, efforts were made to fabricate AlGaN MSM photodetectors prepared on Si substrates. Here the Al0.2Ga0.8N MSM photodetector was characterized for the most part. It was found that dark current of AlGaN PD prepared on Si substrate was much smaller than that of other nitride device on sapphire substrate. With an applied bias of 7 V, it was found that peak responsivity was 0.09 A/W while UV/visible rejection ratio was 324. Moreover, the responsivity of MSM PDs on Si substrate is a function of applied electrical field and can be effectively improved by increasing the bias. Furthermore, conduction mechanism was suspected that carriers need to penetrate the grain boundaries in silicon-substrate MSM PDs. With a 2 V applied bias, the minimum NEP was found to be 3.5 × 10-12 W for Al0.2Ga0.8N MSM PDs, corresponding to the maximum D* of 6.89 × 1011 cmHz0.5W-1.
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LIU, Ching-Yun, and 劉青雲. "High Breakdown Voltage in AlGaN/GaN HEMTs by Using AlGaN/GaN/AlGaN Quantum-Well Electron-Blocking-Layer for Power-Switching Applications." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/39865454238275102167.
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碩士國立臺灣師範大學
光電科技研究所
101
GaN-based high-electron-mobility transistors (HEMTs) are considered to be excellent candidate due to their high sheet-carrier density in the 2-D electron gas (2-DEG) channel and large breakdown field strength (~3.5MV/cm). In this work , we numerically study the enhancement of breakdown voltage in III-nitride HEMTs by employing the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking-layer (EBL) by using APSYS. This concept is based on the superior confinement of two dimensional electron gas (2-DEG) provided by the QW EBL, which results in a significant improvement of breakdown voltage and a remarkable suppression of overflowing electrons, and promotes the mobility of transport electron. The dependence of thickness and composition of QW on the device breakdown is systematically evaluated and discussed in detail for the device optimization. In the present study, the breakdown voltage identified for the conventional HEMT and optimized QW EBL HEMT are 48V and 285V,respectively. Additionally, the QW EBL HEMT structure exhibits the highest electron mobility of 940 cm2/Vs . As a result, we validate the advantages of the proposed structure over the conventional AlGaN/GaN HEMT. We conclude the AlGaN/GaN/AlGaN QW EBL as a promising way to explore the AlGaN/GaN HEMTs in high-speed power-switching applications.
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Lin, Po-Hung, and 林柏宏. "Investigations of the AlGaN films and AlN/AlGaN superlattices grown by Atomic Layer Epitaxy." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/gc6eb9.
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碩士逢甲大學
材料科學所
90
Abstract The purpose of this study is to explore the effects of the growth conditions on the crystal structure, crystallinity and optical properties of the high Al content AlxGa1-xN films and AlN/AlxGa1-xN superlattices. The samples were grown on (0001) sapphire substrates by atomic layer epitaxy. Groups III metalorganics and NH3 were used as the sources of Al, Ga, and N atoms that were carried into the reactor by purified H2. The crystallinity and optical properties of AlxGa1-xN films and AlN/ AlxGa1-xN superlattices(SLs) were investigated by transmission electron microscopy (TEM), x-ray diffractometry(XRD), absorption spectroscopy, and Auger electron spectroscopy(AES). The 0.4 μm thick AlxGa1-xN films exhibited a two-step absorption cut-on edges at 3.5eV and 4.1eV, respectively. This composition separation phenomenon was also revealed by X-ray diffraction measurement, Auger electron spectroscopy and cross-sectional TEM observations. The results of absorption measurement for a set of AlN/ AlxGa1-xN (x~0.5) superlattice structures with various well width of 30 to 65Å and a barrier thickness of 40 Å were reported. The absorption edges of these SLs were observed to decrease monotonously with increment of well width up to 65Å. This result is attributed to the quantum size effect.
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Chen, Yi-Chung, and 陳奕仲. "tudy of Recessed Enhancement-mode AlGaN/GaN/ AlGaN MIS-HEMT with High Threshold Voltage." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/10668624918413250226.
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碩士國立交通大學
材料科學與工程系所
98
AlGaN/GaN/AlGaN enhancement-mode high electron mobility transistor (HEMT) is extensively studied in recent years. However, there is still no solution to fabricate a HEMT with high threshold voltage, which means that it will cause mis-operation in high voltage operation. For enhancement mode operation (E-mode), metal-oxide-semiconductor field effect transistor (MOS-FET), though it has higher threshold voltage, it is not commercialized due to the immature process techniques and higher on-resistance than HEMT. In this thesis, gate recess technique is used to fabricate E-mode AlGaN/GaN/AlGaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). This structure has simpler process and lower on-resistance in comparison with MOS-FET. Additionally, this structure can achieve very high threshold voltage to avoid the mis-operation of the device. Schottky diode was used for process parameter evaluation to find out the optimum process condition, and then the recessed E-mode MIS-HEMT standard process was established. The device demonstrated 2 mA/mm, 0.8 mS/mm, and more than 200V for channel current, transconductance, and three-terminal breakdown voltage, respectively. Furthermore, the device shows 9V threshold voltage. The structure can also be applied to conventional D-mode HEMT application with ID = 280mA/mm and Gm = 75 mS/mm. These characteristics indicate that the structure is promising for high voltage electronic applications.
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Huang, Chong Rong, and 黃崇榕. "High RF Performance AlGaN/GaN High Electron Mobility Transistor with AlGaN Back Barrier Design." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107CGU05124003%22.&searchmode=basic.
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Hsieh, Shyang-Lin, and 謝祥麟. "Atomic Layer Epitaxy of AlGaN." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/48721060772478035277.
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碩士逢甲大學
材料科學學系
87
The purpose of this study is to explore the effect of the growth conditions and substrate orientations on the crystal structure, crystallinity and optical properties of the AlGaN films. AlGaN films were grown on (0001) and (11-20 ) sapphire substrates by atomic layer epitaxy at a temperature range of 950~1050℃. Group III metalorganics and NH3 were used as the sources of Al, Ga, and N atoms that were carried into the reactor by purified H2. The incorporation of Al in the AlGaN films increases linearly with the increment of TMA/(TMG+TMA) ratio in the gas phase. However, increment in Al content tends to result in the formation of microcracks when AlGaN film thickness is beyond its critical layer thickness. Increment in growth temperature is helpful in improving the material quality of AlGaN films. The PL intensity of the yellow emission is greatly reduced as growth temperature increases. In addition to the near bandedge emission and yellow luminescence, a blue emission near 3.0 eV was observed in the AlGaN films grown on the AlN-coated c-Al2O3 substrates. AlGaN/GaN double heterostructures and quantum wells were also successful grown on c-sapphire substrates at 1050℃.
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Te, Teng Yu, and 鄧友德. "Physical Porperties of AlGaN epifilms." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/82499518537182960238.
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碩士國防大學中正理工學院
應用物理研究所
94
In the thesis, we measured and analyzed the dielectric properties of AlGaN epitaxial film. Under the conditions of temperature from 90 K to 460 K and frequency of external electric field from 20 Hz to 1 MHz, the capacitance and dissipation factor of AlGaN epitaxial film were measured. We observed that dielectric properties provide much information about crystal, such as phase transition, defects and activation energy, etc. We also observed the Debye-like relaxation of AlGaN epitaxial film, which is a process of heat-activation. The activation energy obtained from the capacitance and dissipation factor measured is consistence. It is found that the activation energy increases with increasing Al content. It is because increasing Al content makes the lattice mismatch between AlN and GaN increase that more activation energy is needed to thermal-excite carriers to a 2D electric system. In addition, we discussed the carrier transport mechanism. By analyzing the data, we believe that the transport mechanism in the thin film can be interpreted in terms of correlated barrier hopping (CBH) model.
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Lin, Shih-Wei, and 林世偉. "Growth and characterization of AlGaN films and AlGaN/GaN heterostructures on (11-20) Al2O3 substrates." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/05465103103106849884.
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碩士逢甲大學
材料科學所
93
The purpose of this study is to explore the characteristics of AlGaN films and AlGaN/GaN heterostructures grown on (11-20) Al2O3 substrates using atomic layer epitaxy. Trimethylaluminum (TMA), trimethylgallium (TMG) and ammonia (NH3)were used as the sources of Al, Ga, and N atoms that were carried into the reactor by purified H2. The surface morphology, crystallinity and optical properties of AlGaN films and AlGaN/GaN heterostructures were characterized by Nomarski interference optical microscopy , scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffractometry (XRD), and absorption spectroscopy. The experimental results indicate that the properties of the AlGaN films and AlGaN/GaN structures deposited on the (11-20) Al2O3 substrates are comparable to those of the films and structures grown on the (0001) Al2O3 substrates. From the results of TEM diffraction patterns, AlGaN films were found to exhibit certain crystallographic relationship with (11-20) Al2O3 substrates. The <0001>AlGaN and <01-10>AlGaN were found to be in parallel to <11-20>sapphire and <01-10>sapphire, respectively.
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Kun-Ta, Wu. "Electrical transport in AlGaN/GaN heterostructures." 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2007200523291100.
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Hong, Y. H., and 洪一航. "The characteristics of AlGaN/GaN heterostructure." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/36918171770845236815.
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碩士長庚大學
電子工程研究所
94
AlGaN/GaN heterostructure field-effect transistors (HFETs) have been a subject of intensive investigation recently and have emerged as attractive candidates for high voltage, high-power operation at microwave frequencies, such as low noise microwave amplifier、 power microwave amplifier、 high temperature devices and power suppliers. In this work, we have grown AlGaN/GaN hetero-structures on Sapphire and Si substrates by Metal Organic Chemical Vapor Deposition (MOVPE) respectively. In order to investigate the effect of Si-doped GaN layers on the performance of AlGaN/GaN heterostructures, two groups of AlGaN/GaN with Si-doped GaN layers were studied. One group was grown on Si substrates while the other on sapphire. Properties of the samples are governed by the two-dimensional electron gas (2DEG) formed in the AlGaN/GaN hetero-junctions, which can be characterized by mobility, sheet carrier concentration and resistance. I-V and C-V properties of AlGaN/GaN hetero-junctions were analyzed. Comparison of mobility and depth-profile between doped and un-doped samples in two groups were made. Details will be discussed in the thesis.
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Shao-Tang, Lien, and 連少棠. "AlGaN/GaN grown on different substrates." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/47483384979539988291.
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碩士長庚大學
電子工程研究所
93
We have studied AlGaN/GaN heterostructures grown on different substrates. The electrical, optical and structural properties were analyzed and correlated with the difference in structures and with the substrates used. Several nominally undoped AlGaN/GaN heterostructures with different Al percentage were first grown on the sapphire substrates. We have observed that increasing Al percentage in the heterostructures induced a higher reverse current and a higher charge density in channel. As the carrier concentration increased, the charge distribution shifted closer to the heterointerface, with the electron transport becoming more sensitive to the interface roughness scattering. The room-temperature electron mobility gradually decreased with the increasing carrier density. Both the interface roughness scattering and alloy disorder scattering are expected to decrease the low-temperature electron mobility. Several nominally undoped AlGaN/GaN heterostructures with different buffer layers were grown on the silicon substrates. Different buffer layers induced different stress states at the heterointerface. The heterointerface showed a more serious strain relaxation from the stronger tensile strain, different samples showed different room-temperature carrier densities and electron mobility. The sample with the simplest structure showed the lowest carrier density and electron mobility. The sample with a SiN interlayer showed the highest carrier density and electron mobility. The reverse current rapidly increased after a complete depletion of the channel using I-V and C-V measurements, indicating likely defects in the channel. Due to the interaction of defect level and conduction band, the carrier density varied with decreasing temperature. We have also observed the DAP recombination using low-temperature PL measurement for the samples grown on silicon substrates. The 2DEG electron mobility decreased with increasing DAP recombination .We suggest that the DAP acted as a trap level at low temperature, that would reduce the electron mobility. We also suggest that the DAP are consistent with the N vacancy and N interstitial caused by the tensile strain present.
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李奕辰. "Novel Light Emitting AlGaN/GaN HEMT." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/7efx9a.
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Wu, Kun-Ta, and 吳坤達. "Electrical transport in AlGaN/GaN heterostructures." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/36668486823763821097.
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碩士國立臺灣大學
物理研究所
93
In this thesis, I will report on two measurements on AlGaN/GaN high electron mobility transistors (HEMTs). This thesis consists of the following two parts. 1.Transport in AlxGa1-xN/GaN HEMTs with different Al compositions We performed measurements on three AlxGa1-xN/GaN HEMTs with different Al contents (11%, 15%, and 25% respectively). All three samples are grown on sapphire substrates, and the mobility measurements indicate that AlxGa1-xN/GaN HEMTs with 15% Al content have the highest mobility (6600 cm2/Vs at 10K). If the Al content of AlxGa1-xN/GaN HEMTs exceeds 15%, the mobility will drop drastically. In addition, we found that the mobilities of the three samples are almost identical at room temperature. This is because electron-phonon scattering dominates the electrical scattering at room temperature, and the electron-imperfection scattering due to impurities in the sample is small compared with electron-phonon scattering. Furthermore, we found that the 2DEG concentration increases with increasing Al content in AlxGa1-xN. Quantitative calculation of the 2DEG concentration was performed and the same trend was obtained. The reason for this is that when the Al fraction increases, the polarization in AlxGa1-xN increases and induces more sheet charges at the interface of AlxGa1-xN and GaN. Therefore, for an AlxGa1-xN/GaN heterostructure with a higher Al composition, more electrons would be attracted to compensate for the sheet charges near the AlxGa1-xN/GaN interface. Hence the 2DEG concentration would be higher for an AlxGa1-xN/GaN sample with a higher Al composition. We also measured the activation energy of AlxGa1-xN/GaN HEMTs, and found that the activation energy increases with increasing Al content. As the Al content increases, the lattice mismatch between AlxGa1-xN and GaN becomes more prominent. This increased lattice mismatch could induce a larger defect density. Therefore a higher activation energy is required to thermally activate the carriers into the 2DEG region. Finally, the fact that AlxGa1-xN/GaN HEMTs with 15% Al content has the highest mobility suggests that we can grow other AlGaN/GaN HEMTs with 15% Al content for the greatest mobility. 2.Measurements of AlGaN/GaN HEMTs grown on p-type silicon substrates The substrate used in the previous section is sapphire. However, sapphire is not as popular as Si in the industry. We therefore attempt to grow our samples on Si substrates. However, growing high-quality GaN on silicon substrates proves difficult because of the large lattice mismatch (about 17%) and large thermal mismatch (about 54%) between Si and GaN. In this section, we inserted a thin Si5N4 film with deposition time of 5 seconds and 10 seconds to improve the GaN quality, and observed how such a thin film could affect the 2DEG mobility at the interface of AlGaN and GaN in comparison with the case without a Si5N4 thin film. At 10 K, the sample without the Si5N4 thin film had mobility 744 cm2/Vs, whereas for the samples with 5 seconds and 10 seconds deposition time of Si5N4 it was 2323 cm2/Vs and 2387 cm2/Vs respectively. The result showed that the mobility was greatly enhanced by as much as three times after the Si5N4 thin film was inserted. Upon comparing the mobility with the results of the previous chapter, we see that Al0.15Ga0.85N/GaN HEMTs on sapphire substrates had a much higher mobility of 6600 cm2/Vs. We conclude that it is difficult to grow AlGaN/GaN HEMTs on silicon substrates with mobilities as high as those grown on sapphire substrates. Nevertheless, this great enhancement of the mobility demonstrates the usefulness of our technique. If we perform further investigations on the optimization of our growth temperature, HEMT structure, and most importantly, Si5N4 treatment technique, it is expected that the quality of HEMTs grown on Si substrates may well be as high as those grown on conventional sapphire substrates.
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Lee, Jheng-Wei, and 李政威. "Optical properties of AlGaN/GaN heterostructures." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/24255202410895775045.
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碩士國立東華大學
光電工程研究所
96
In this thesis, the optical properties of several wurtzite AlGaN/GaN heterostructures have been characterized by photoluminescence(PL), thermo-reflectance(TR) and contactless electroreflectance(CER) measurements. Because the special polarization effects that dissimilar to the groups of GaAs heterostructrres, the AlGaN/GaN heterostructures generate automatically the two-dimentional electron gas(2DEG) at the interface of AlGaN and GaN without modulation doping. From PL measurements, we can observe the A(heavy hole state), B(light hole state) and C(crystal-field split band) excitonic transitions, which are due to the crystal field effects and the spin-orbital interaction at Γ of the central Brilliouin zone that results in the splitting of valence bands, Γ9, upper Γ7 and lower Γ7. We can also observe the direct transitions of GaN and AlGaN. In different samples, especially the doped and the undoped GaN layer or AlGaN layer, the full spectral width at half maximum(FWHM) are influnced by the doping concentration, if a sample is undoped, its FWHM would be narrower than a doped one, in addition, the peak is shaper. By using the Bose-Einstein equation, we can fit the temperature-dependent relationship of transition energies. Through the fitting result, we can see that the energy position would shift to a higher place as the temperature goes down, because of the phonons and the electrons(excitons) interaction. In other words, it’s a blue-shift appearance. Another part, in the TR spectrum, we can discover the below band-edge interference in the layer of each sample, the oscillation strength grows stronger when the energy range is near to the band gap, and the period is shorter at the same time. It’s special to discover that at the room temperature, the transitions of the AlGaN layer, is not visible in the PL spectrum while they are present at 300K. The TR spectrum also show the blue-shift appearance with the decrease of temperatures. FKOs are observed in the CER spectrum, the spectral oscillations appears higher than the energy gap. By using the linear regression estimate, we can obtain the nth extreme of FKOs, if we take the band gap and the effective masses of electrons and holes, another important information will be find: build-in electric field.
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Lin, Wei-Tse, and 林瑋哲. "AlGaN/GaN HEMTs with Backgate Structure." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/a3hpr2.
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碩士國立中央大學
電機工程學系
105
This study discusses the impact of back-gate structure on the DC characteristics of an AlGaN/GaN high-electron mobility transistor (HEMT). There are two parts in this study: (1) An AlGaN/GaN/AlGaN double heterostructure is designed to form two dimensional electron gas (2DEG) channel and two dimentional hole gas (2DHG) backgate and investigate the reduction of leakage current with shift of threshold voltage when backgate bias is applied. (2) AlGaN/GaN HEMTs with p-GaN backgate were annealed for 15 minutes in N2 ambient at 700℃. After annealing, we investigate the ability of activated p-GaN backgate layer for controling threshold voltage, reducing leakage current, and enhancing breakdown voltage. The results of simulation reveal that 2DHG backgate can decrease leakage current and turn device from depletion-mode operation to enhancement-mode operation by applying backgate bias. However, the fabricated devices do not demonstrate the same control capibility of threshold voltage as simulation due to the bad connection between backgate metal and 2DHG. The large electric field induced by backgate still can suppress device leakage current when a negative bias is applied. The on/off current ratio in different backgate bias can achieve 107. In addition, device breakdown voltage of 691 V is observed. For the DC characteristic of AlGaN/GaN HEMTs with p-GaN backgate, devices without annealing have lower leakage current and on-state resistance. Devices with annealing show higher leakage current and more obvious positive shift of threshold voltage. The shift of threshold voltage for device without annealing is 0.46 V between backgate bias 0 V and -14 V, and off-state leakage current reduction is 42.6%. The shift of threshold voltage for device with annealing is 0.55 V between backgate bias 0 V and -14 V, and off state leakage current reduction is 73.1%. The on/off current ratio for device without annealing is 5.47×107, and 8.86×105 for device with annealing when backgate bias apply 0 V. Current ratio for device with annealing can increase to 1.12×107 when backgate bias at -14 V. Devices without annealing show lower leakage current before devices breakdown. However, devices with annealing show higher breakdown voltage. The highest breakdown voltage is 762 V for device with annealing when applying backgate bias of -14 V.
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Chi-ChihTseng and 曾致齊. "Investigation of AlGaN/GaN MOS-FinHEMT." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/t9c92q.
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Lin, Tien-Kun, and 林天坤. "Photo-CVD SiO2 Layers on AlGaN and AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field Effect Transistor (MOSHFET)." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/87764962774265421974.
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碩士國立雲林科技大學
電子與資訊工程研究所碩士班
91
High quality SiO2 is successfully deposited onto AlGaN by photo chemical vapor deposition (photo-CVD) using a D2 lamp as the excitation source. We are verified the high quality SiO2 film by the analysis of the chemical and physical characteristics such as AFM, FTIR, XPS and AES instruments. It is found that the interface state density of Photo-SiO2 is only 1.1�e1011 cm-2eV-1 and the oxide leakage current that is dominated by Poole-Frenkel emission transport mechanism is only~10-7A/cm2 with an applied field of 4 MV/cm. Furthermore,. we confirm the photo-SiO2 have the good thermal stability by refractive index, C-V and I-V measurement while the annealing temperature is up to 400oC. AlGaN/GaN metal-oxide-semiconductor heterojunction field effect transistors (MOSHFETs) are also fabricated with such photo-CVD oxide as the insulating layer. Compared with AlGaN/GaN metal-semiconductor HFET (MESHFETs) with similar structure, we find that we can reduce the gate leakage current by more than four orders of magnitude by inserting the photo-CVD oxide layer in between AlGaN/GaN and gate metal. With a 1 �慆 gate length, it is found that the maximum saturation current (Idmax), maximum transconductance (gmmax) and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET are 800 mA/mm, 86 mS/mm and 9 V, respectively. Furthermore, it is also found that while devices are operated at 300oC Idmax , leakage current, maximum gm and GVS are kept at 580 mA/mm and 9.7 mA/mm, 65 mS/mm and 8.5 V, respectively. Such a result implied our device is a good candidate for application in hash environment.
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Hu, Bo-Yuan, and 胡柏元. "Two-dimensional electron gas behavior of crack-free AlGaN/GaN HEMT on Si substrate using AlGaN grading layers." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/27306993418857263411.
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碩士國立彰化師範大學
電子工程學系
102
We present the study of crack-free AlGaN/GaN HEMTs on Si substrate grown by metalorganic chemical vapor deposition with the presence of two-dimensional electron gas (2DEG). In this study, three AlxGa1-xN /GaN HEMTs on Si with similar structure are analyzed and marked A, B and C. In addition, we detect the behavior of 2DEG by employing a series of optical and electrical measurements. The band gap energy of GaN and AlxGa1-xN are also identified based on the reflectance (R) and photoluminescence (PL) spectra. Therefore, the Al compositions are determined to be 25, 30 and 30% for sample A, B and C, respectively. In addition, crack-free GaN on Si is confirmed by the images of SEM for sample A, B and C. According to reciprocal space mapping of X-ray diffraction for sample A to C, the thin top AlGaN layer are observed to be fully strained on the thick GaN buffer layers where the graded AlxGa1-xN layers are fully relaxed. The fitted strength of electric field at the top AlGaN layer through electrolyte electro-reflectance (EER) spectra is about 731, 979 and 655 kV/cm for sample A to C, respectively. The sheet 2DEG concentration measured using EER technique and Hall measurement are both close to 1.1×1013, 1.4×1013 and 1.4×1013 cm-2 which are in excellent agreement with the theoretical value under specific AlGaN thickness and Al composition (~1.1×1013 cm-2 for sample A; ~1.4×1013 cm-2 for sample B and C). In addition, PL spectra at room temperature prove the epitaxy quality for GaN layer is great for sample A to C owing to its narrow full widths at half maximum. In addition, we develop an integrated and automatically measuring system for optical characteristics measurement. The system is named after “OSM”, which pronounce like the word “awesome”. Most of the measurements conducted in this study are achieved by this system, including R, EER, PL measurements etc.
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Wang, Sheng-Chih, and 王勝志. "Electroreflectance spectra of AlGaN/AlN/GaN heterostructure." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/y284p4.
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碩士國立中山大學
物理學系研究所
96
Electroreflectance spectra of AlGaN/AlN/GaN heterostructures were measured at various biased voltages (Vdc). Strengths of the internal electric field in AlGaN (FAlGaN) were evaluated from periods of Franz-Keldysh oscillations (FKOs), which were observed above band-gap energy of AlGaN. The relation between FAlGaN and Vdc exhibits an anomalous behavior, which is different from the previous results of the AlGaN/GaN heterostructure. It agrees with the theoretical result of a Poisson-Schrödinger calculation, which shows that two dimensional electron gas (2DEG) exists not only in quantum well (QW) at AlN/GaN interface, but also in QW at AlGaN/AlN interface. This is also consistent with electron-density distribution obtained by capacitance-voltage measurements. When Vdc becomes more negative, the previous mechanism of depleting 2DEG is through flatting one side of QW. However, it was found that the depletion of 2DEG can also occur when the top of valence band at surface becoming higher than bottom at QW.