Rozprawy doktorskie na temat „IR photodetector”

Thesis (M.S. in Combat Systems Technology)--Naval Postgraduate School, Dec. 2004.
Thesis Advisor(s): Gamani Karunasiri, Richard C. Olsen. Includes bibliographical references (p. 57-60). Also available online.

Le PtSe₂ est un matériau 2D de la famille des dichalcogénures de métaux de transition (TMDs) qui présente des propriétés intrinsèques exceptionnelles : mobilité des porteurs de charge élevée (200 - 450 cm².(V.s)⁻¹), gap électronique ajustable en fonction du nombre de monocouches (MLs), absorption optique large bande et excellente stabilité à l'air. Ces propriétés sont idéales pour des applications (opto)électroniques. Cependant, la croissance de PtSe₂ de haute qualité cristalline sur un substrat à bas coût et isolant reste un enjeu majeur. Ici, la synthèse de PtSe₂ bicouche à multicouche (< 20 MLs) par épitaxie par jets moléculaires (MBE) est optimisée sur un substrat de saphir. Les caractérisations systématiques comprennent la diffraction électronique (RHEED), la spectroscopie Raman, la spectroscopie de rayons X à dispersion d'énergie (EDS) et des mesures électriques de conductivité. Pour les films épais de PtSe₂ semi-métallique, on démontre que des températures élevées de croissance (520 °C) et de recuit (690 °C), ainsi qu'un fort flux de sélénium (Ф(Se) = 0,5 Å.s⁻¹ ; Ф(Se)/Ф(Pt) ~ 170), permettent d'obtenir une haute qualité cristalline et une haute conductivité électrique. L'impact du recuit post-croissance sur les propriétés structurelles des films épais est particulièrement étudié par diffraction des rayons X (XRD) et microscopie électronique à transmission (STEM). Les films de PtSe₂ non recuits consistent en une distribution 3D de domaines superposés ayant différentes orientations dans le plan, tandis que les films recuits consistent en un réseau 2D de domaines monocristallins selon l'axe c. En d'autres termes, les films non recuits ont des domaines d'épaisseur plus faible que celle du film et sont constitués de phases semi-conductrices et semi-métalliques, entraînant une faible conductivité (0,5 mS). Au contraire, les films recuits sont composés uniquement de domaines quasi-monocristallins et semi-métalliques, et présentent une très haute conductivité, jusqu'à 1,6 mS. On montre également que l'indicateur de qualité cristalline couramment utilisé, qui est la largeur à mi-hauteur (FWHM) du pic Raman Eg, n'est valide que s'il est étudié conjointement avec la FWHM du pic Raman A1g. On démontre que plus la FWHM des pics Eg et A1g est faible, plus la qualité cristalline des films de PtSe₂ dans le plan et hors du plan, respectivement, est élevée, et plus la conductivité électrique augmente. Concernant les films bicouches de PtSe₂ semi-conducteur, on obtient des films de haute qualité cristalline, dont la FWHM des pics Eg et A1g est comparable à celle des cristaux exfoliés, en effectuant une synthèse avec un flux périodique de Pt (periodic supply epitaxy). Les films de PtSe₂ bicouches à multicouches ne sont pas monocristallins mais présentent une texture de fibre selon l'axe c, ce qui est typique sur un substrat de saphir. On démontre pour la première fois l'épitaxie d'un film épais de PtSe₂ sur des surfaces vicinales (marches) de saphir. Pour finir, nous avons fabriqué des dispositifs optoélectroniques fonctionnant à 1,55 µm, la longueur d'onde typique des télécommunications par fibre optique. Ils sont à base de PtSe₂ épais semi-métallique, présentant une haute conductivité électrique et une bonne absorption optique à 1,55 µm, qui est directement synthétisé sur un substrat de saphir 2 pouces. On montre des photodétecteurs à base de PtSe₂ avec une largeur de bande record de 60 GHz et le premier mélangeur optoélectronique à base d'un TMD présentant, de plus, une largeur de bande supérieure à 30 GHz
PtSe₂ is a 2D material from the transition metal dichalcogenide (TMD) family that exhibits outstanding intrinsic properties: high charge carrier mobility (200 - 450 cm².(V.s)⁻¹), tunable bandgap with the number of monolayers (MLs), broadband optical absorption and excellent air stability. These properties are ideally suited for (opto)electronic applications. However, the growth of high crystalline quality PtSe₂ on low-cost and insulating substrates remains a major challenge. Here, the synthesis of bilayer to multilayer PtSe₂ films (< 20 MLs) by molecular beam epitaxy (MBE) is optimized on a sapphire substrate. The systematic characterizations include electron diffraction (RHEED), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX) and electrical conductivity measurements. For thick semimetallic PtSe₂ films, we demonstrate that high growth (520°C) and annealing (690°C) temperatures, combined with a high selenium flux (Ф(Se) = 0.5 Å.s⁻¹; Ф(Se)/Ф(Pt) ~ 170), leads to high crystalline quality and high electrical conductivity. In particular, the effect of the post-growth annealing on the structural properties of the thick films is investigated using X-ray diffraction (XRD) and transmission electron microscopy (STEM). We show that non-annealed PtSe₂ films consist of a 3D random distribution of superimposed domains with different in-plane orientations, while the annealed films consist of a 2D network of single-crystalline domains along the c-axis. In other words, non-annealed films have domains with a thickness smaller than that of the film and are composed of both semiconducting and semimetallic phases, resulting in low electrical conductivity (0.5 mS). In contrast, the annealed films are composed solely of quasi-single-crystalline and semimetallic domains, and exhibit high conductivity, up to 1.6 mS. We also show that the commonly used crystalline quality indicator, which is the full width at half maximum (FWHM) of the Eg Raman peak, becomes a reliable metric only when it is studied in conjunction with the FWHM of the A1g Raman peak. We demonstrate that the lower the FWHM of both the Eg and A1g peaks, the higher the crystalline quality of the in-plane and out-of-plane PtSe₂ films, respectively, and the higher the electrical conductivity. For semiconducting PtSe₂ bilayer films, high crystalline quality films with Eg and A1g FWHM values comparable to those of exfoliated crystals are obtained using a periodic Pt flux (periodic supply epitaxy). The bilayer to multilayer PtSe₂ films are not monocrystalline but present a fiber texture along the c-axis, which is typical on a sapphire substrate. The epitaxy of a thick PtSe₂ film on vicinal sapphire surfaces (steps) is demonstrated for the first time. Finally, we fabricated optoelectronic devices operating at 1.55 µm, the typical wavelength of optical fiber telecommunications. They are based on thick semi-metallic PtSe₂, exhibiting high electrical conductivity and good optical absorption at 1.55 µm, which is directly synthesized on a 2-inch sapphire substrate. We demonstrate PtSe₂-based photodetectors with a record bandwidth of 60 GHz and the first TMD-based optoelectronic mixer with, in addition, a bandwidth larger than 30 GHz

This thesis deals with electrical and optical characterization  of p+i–n+ nanowire-based photodetectors/solar  cells. I have investigated their I-V performance and found that all of them exhibit a clear rectifying behavior with an ideality factor around 2.2 at 300K.  used Fourier transform infrared spectroscopy to extract their optical properties. From the spectrally resolved photocurrent data, I conclude that the main photocurrent is generated in the i-segment of the nanowire (NW) p-i-n junctions, with negligible  contribution from the substrate.   I also used a C-V technique to investigate the impurity/doping profiles of the NW p+-i-n+ junction.  The technique has been widely used for investigations of doping profiles in planar p-n junctions, in particular with one terminal (n or p) highly doped. To verify the accuracy of the technique, I also used a planar Schottky  sample with an already known doping profile for a test  experiment. The result is very similar to the actual data. When we used the technique to investigate the doping level in the NWs photodetectors grown on InP substrates, the results show a very high capacitance above 800pF which most likely is due to the influence of the parasitic capacitance from the insulating layer of SiO2. Thus,  a new sample design is required to investigate the  doping profiles of NWs.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.
Includes bibliographical references (leaves 129-132).
Strain-balanced silicon-germanium superlattices grown on high quality compositionally graded buffers, or virtual substrates. make a complete range of alloy composition and biaxial strain combinations accessible. This structure is a unique way to achieve high quantum efficiency near IR photodetection for silicon-based optical interconnects. The growth of the strain-balanced superlattices by molecular beam epitaxy (MBE) and ultra high vacuum chemical vapor deposition (UHV-CVD) is presented and the role of adsorbed hydrogen during UHV-CVD growth is addressed. Hydrogen adsorption 0,1 the growth surface proved a useful technique to minimize coherent strain relaxation at the higher growth temperatures required for UHV-CVD silicon-germanium growth. The near IR absorption spectrum of the strained silicon-germanium materials possible using strain-balanced superlattices is critically required in the design of a photodetector. A model based on deformation potential theory and semiconductor absorption physics is used to predict the absorption coefficient as a function of strain and alloy composition. Photocurrent junction spectroscopy of strain-balanced silicon­germanium materials is used to confirm the results of the model. The effects of threading dislocations associated with the compositionally graded buffers on the bulk leakage current of photodiodes is determined using electron-beam induced current imaging techniques to measure dislocation density. The correlation between dislocation density and leakage current yielded a current per dislocation line length of 200 pA [mu]m·1. Coupling strategies for the integration of high dielectric contrast polycrystalline silicon/ Si02 strip waveguides and silicon-germanium photodetectors are presented. The high optical power densities possible with the polycrystalline silicon waveguides permits the miniaturization of photodetectors. The effects of integration and miniaturization on photodetector performance are discussed.
by Laura Marie Giovane.
Ph.D.

Photodetectors are a kind of semiconductor devices that convert incoming light to an electrical signal. Photodetectors are classified based on their different structure, fabrication technology, applications and different sensitivity. Infrared photodetectors are widely used in many applications such as night vision, thermal cameras, remote temperature sensing, and medical diagnosis etc.   All detectors have material inside that is sensitive to incoming light. It will absorb the photons and, if the incoming photons have enough energy, electrons will be excited to higher energy levels and if these electrons are free to move, under the effect of an external electric field, a photocurrent is generated.   In this project Fourier Transform Infrared (FT-IR) Spectroscopy is used to investigate a new kind of photodiodes that are based on self-assembled semiconductor nanowires (NWs) which are grown directly on the substrate without any epi-layer. The spectrally resolved photocurrent (at different applied biases) and IV curves (in darkness and illumination) for different temperatures have been studied respectively. Polarization effects (at low and high Temperatures) have been investigated.  The experiments are conducted for different samples with high concentration of NWs as well as with lower concentration of NWs in the temperature range from 78 K (-195ºC) to 300 (27ºC). These photodiodes are designed to work in near infrared (NIR) spectral range.   The results show that the NW photodetectors indeed are promising devices with fairly high break down voltage, change of photocurrent spectra with polarized light, low and constant reverse saturation current (Is). The impact of different polarized light on photocurrent spectra has been investigated and an attempt has been made to clarify the observed double peak of InP photocurrent spectrum. Our investigations also include a comparison to a conventional planar InP p-i-n photodetector.

碩士
國立清華大學
電機工程學系
85
The purpose of this thesis is to fabricate a-SiGe:H IR detectors. Two mainefforts of this thesis are (1)fabrication of a-SiGe:H films. (2)NIPIN IR photodetectors. In order to reduce the influence of the particulate formation in thepreparation of a-SiGe:H films, high hydrogen dilution ratio which is about93 % and pulse RF power is used for a-SiGe:H films. The particulate formationis decreased by using pulse RF power. The device structure of a-SiGe:H photo detector is NIPIN barrier type phototransistor. The I layer which light is first incident is the visible lightabsorption region and the other is the IR light absorption region.The photo to dark current ratios of this device under 780 nm LED illumination is over 100 and the photocurrent is over 1 uA which is enough for the requirement for the circuit design.

碩士
國立海洋大學
電機工程學系
87
-Abstract- In this experiment, we use the low cost IR-CVD system and two-step growth method to grow ZnSe epilayers on oriented-(111) Si substrate for reducing the lattice mismatch problem between ZnSe and Si. Because of the existence of the lattice constant mismatch within approximately 4.1% between the ZnSe and Si that can introduce high density of threading dislocations, stacking faults and defects resulting in the interface states. We use the optimum ZnSe epilayers on Si to fabricate the devices of MSM photodetector. Further, we have shown that planar metal-semiconductor-metal photodetectors on ZnSe/Si are promising candidates for optoelectronic integration of short-wavelength components. We report the Au-ZnSe/Si MSM photodetector without any passivation and antireflection coating exhibits the photo-responsivity are 5.21A/W at 470nm light wavelength, 4.77A/W at 500nm light wavelength and 1.64A/W at 650nm light wavelength at 10V bias. In addition, we obtained the strongest photo-responsivity in the wavelength of 470nm. The results demonstrate the studying ZnSe/Si MSM photodetector will be suitable for the applications of the short wavelength photo-detectors. We can measurement yielded an FWHM of 25ns for a bias voltage of 10V. Moreover, we estimated a bandwidth of about 22 MHz. The conventional liner interdigitated electrode MSM and the 2D grid of the alternative approach pattern were been fabricated. Therefore, we obtained larger photo-responsivity for TM polarisation than TE polarisation result of the grating effect. The orthogonal directions with interdigitated fingers of polarisation refer to light polarised parallel (TE) result to the centre stem reflect by the metal grating. Thus, the convention and 2D grid of the alternative approach pattern MSM photodetectors depend on the angle of polarised that is polarisation-sensitivity. There is virtually no obviously difference in the response behavior between the conventional linear electrode and 2D grid of the alternative approach detectors. We can obvious the thickness absorption layer increase and the MSM photo-responsivity increase. This is because the thicker absorption layer will generate more photo carrier in the deep absorption layer due to a larger number EHPs can pass through the absorption layer and arrive to the electrode. Therefore, the MSM photodetector photo-responsivity depends on the thickness of the absorption layer. Nevertheless, the photo-responsivity of dependence on wavelength decrease with the absorption layers thickness increase. Because more light passes through the absorption layer into the substrate is due to the thinner absorption layer and result in lower spectral response in the blue-green range. A thinner ZnSe layer enables to eliminate the longer carrier paths that loop down into the absorption material. Although, decrease the absorption layer will increase the impulse response time which depend on bandwidth but will result to photo-reponsivity decrease. Therefore, the performance of the requirement determines to the absorption layer thickness. We report the Au-ZnSe/Si MSM photodetector without any passivation and antireflection coating and we obtain the high performance of photo-responsivity. It is evident that the absorption area increase and the photocurrent were created increase. And when the absorption areas decrease that the photo-responsivity is exponential decay. In addition, the impulse response time as a function of the interdigital spacing width was measured with bias of 10V. The FWHM is dependent on the spacing width and carrier velocity limited the transit time. Then the bandwidth of the Au-ZnSe/Si MSM photodetector was obtained versus spacing gap relation is based on a fit to experimental results. In addition, we employed the low cost CVD system and Si as the substrate due to the advantages such as high thermal conductivity, large-area, low-cost wafers and mechanical hardness. Those made us easier to achieved low cost short wavelength blue light opto-electronic devices and more useful for the applications of the opto-electronic integrated circuit (OEIC).

碩士
國立成功大學
電機工程研究所
84
In this thesis , the amorphous silicon-germanium / crystal silicon heterojunction high-speed IR photodetector was studied in detail. In preparing the samples , the amorphous silicon- germanium alloys were grown on the crystal silicon subtrate by plasma enhanced chemical vapor deposition (PECVD). Both advantages of the low resistivity and high mobility characteristics of crystal silicon and the low temperature preparation processing,high optical absorption ,large area device feasibility and low cost of amorphous silicon are employed to prepare the heterojunction structure photodetector for faster response speed and lower cost. Compared with the traditoinal amorphous silicon germanium structure,the device with the structure of Al/n-a-Si:H/i-a- Si0.6 Ge0.4:H/p-c-Si has the following advantages: 1.The absorption wavelength peak moves to a higher value(865 nm ) than that 710 nm of the traditional amorphous silicon germanium structure. 2.The device has a faster response speed ( with a rise time of 195μs ) than that ( with a rise time of 465μs ) of the traditional amorphous silicon germanium structure . 3.The dark current has been decreased to a lower value (3.3μA under a reverse bias of 5V ) than that ( 50μA under the same bias)of the amorphous silicon germanium structure.

碩士
國立成功大學
電機工程研究所
83
In this thesis, an high optical gain amorphous silicon germanium alloy IR photodetector with Bragg reflectors has been developed by plasma enhanced chemical vaporphase deposition( PECVD). By using Bragg reflectors ,we can reabsorb the unabsorbed light to increase absorption efficiency , thus we can increase the optical gain. In addition, the Bragg reflector structure will serve as a barrier to block the outdiffusion of defects from the substrate into the active region of the detector which contributes to lower dark current. Therefore, under the same dark current condition, the PIN photodetector with Bragg reflectors can be operated with large voltage bias to increase the avalanche multiplication which will contribute higher optical gain. Based on experiment results, we find that the photodetector with Bragg reflectors has better characteristis than the conventional photodetector The full width of half magnitude(FWHM) can be reduced from 250nm to 150nm .The optical gain under 25uA can be attained as high as 328 with an incident light power of 1uW . Additionally,the rise time of this device is increased from 750us to 942.5us .

碩士
國立交通大學
光電工程系所
97
Through Doping of Near-IR(NIR) materials in organic Photodiodes, the absorption of the device was extended into long wavelength region. Because the NIR dye can trap the charges easily, the trapped carrier will induce an electric field and decrease the injection barrier of the apposite charges. Therefore, high photocurrent multiplication was achieve at higher reverse bias. The turn on voltage of the photomultiplication did not depend on the light intensity. However, the degree of phase separation and the thickness of active layer significantly affected the turn on voltage. Finally, we found that the dark current increased with the surface roughness of the active layer.

碩士
國立海洋大學
電機工程學系
88
Abstract In this thesis, the low cost IR furnace chemical vapor deposition system is used to obtain the ZnSe epilayer. The analysis of the ZnSe epilayers quality including the crystallographic properties was demonstrated by XRD, the analysis of the surface morphologies and the thickness was observed by SEM, the composition depth profiles was measured by SIMS and the discussion of optical characteristics was determined by PL measurement. Planar metal-semiconductor-metal (MSM) photodetector have been noted recently, however, the photocurrent and photoresponsivity of such photodetector are limited due to the blocking of incident light by conventional Schottky metals. To improve the photoresponsivity of ZnSe photodetector, the tin-doped indium oxide (ITO) transparent electrode is used as electrode in this paper. In this experiment, the ITO film was deposited at room temperature by RF magnetron sputtering on the top of ZnSe as an electrode. After deposited, the ITO film is annealed in an oxygen ambience at 400oC. After annealing, the transmittance of ITO film from 82.5﹪raise to 90.1﹪and the electrical resistivity of ITO film form 4.5E-1 low to 2.8E-3. C-V measure is used to calculate the carrier’s concentration of ZnSe epilayer. The carrier concentration of the as grown ZnSe epilayer is 2.91×1013cm-3. The barrier height of the Au/ZnSe/PSL Schottky barrier can also be estimated is 1.4eV and the barrier height of the ITO/ZnSe/PSL Schottky barrier is 1.35eV. The Au ZnSe MSMPD and ITO ZnSe MSMPD show a very high performance of spectral response on short-wavelength region. The photo–responsivity of the Au ZnSe MSMPD is 4.61A/W and the photo–responsivity of the ITO ZnSe MSMPD is 6.94A/W at 470nm light wavelength with fix incident light 0.367mW. The impluse response of the MSMPD is 23ns for a bias voltage of 10V and we calculate a bandwidth of about 23.5 MHz. In this thesis, we studied and fabricated the metal-semiconductor– metal photodetector devices based on ZnSe material using low cost IR furnace CVD system. To improve the performance of photodetector, we employ indium tin oxide as transparent electrodes with high Schottky barrier contacts with ZnSe. It will be helpful to obtain cheaper short wavelength blue light photodetectors and high responsivity blue light photodetectors. In recent year, a great deal of efforts has been devoted to the development of OEIC technique. The wide bandgap ZnSe epilayer was grown on Si substrate by using low cost CVD system will show a great potential for the applications of the short wavelength OEIC.