Dissertations / Theses on the topic 'P-type GaAs'

In this thesis we study GaAs one dimensional hole systems with strong spin-orbit interaction effects. The primary focus is the Zeeman splitting of 1D subbands in the two orthogonal in-plane magnetic field directions. We study two types of 1D hole systems based on different (311)A grown heterostructures: a modulation doped GaAs/AlGaAs square quantum well and an undoped induced GaAs/AlGaAs triangular quantum well. The results from the modulation doped 1D wire show enhanced anisotropy of the effective Lande g-factor for the two in-plane field directions (parallel and perpendicular to the wire), compared to that in 2D hole systems. This enhancement is explained by the confinement induced reorientation of the total angular momentum ^ J from perpendicular to the 2D plane to in-plane and parallel to the wire. We use the intrinsic anisotropy of the in-plane g-factors to probe the 0:7 structure and the zero bias anomaly in 1D hole wires. We find that the behaviour of the 0:7 structure and the ZBA are correlated and depend strongly on the orientation of the in-plane field. This result proves the connection between the 0:7 and the ZBA and their relation to spin. We fabricate the first induced hole 1D wire with extremely stable gate characteristics and characterize this device. We also fabricate devices with two orthogonal induced hole wires on one chip, to study the interplay between the confinement, crystallographic anisotropy and spin-orbit coupling and their effect on the Zeeman splitting. We find that the ratios of the g-factors in the two orthogonal field directions for the two wires show opposite behaviour. We compare absolute values of the g-factors relative to the magnetic field direction. For B || [011] the g-factor is large for the wire along [011] and small for the wire along [233]. Whereas for B || [233], the g-factors are large irrespective of the wire direction. The former result can be explained by reorientation of ^ J along the wire, and the latter by an additional off-diagonal Zeeman term, which leads to the out-of-plane component of ^ J when B || [233], and as a result, to enhanced g-factors via increased exchange interactions.

In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.

Polarization behaviours of copper diffused p-type GaAs was studied in 1. 0M NaCl and 1. 0M NaNO₃ by means of pitting scan and linear sweep potentiodynamic polarization techniques. The thermodynamic potential-pH diagram of the GaAs-H₂O system was constructed. The observed electrode behaviours of GaAs were compared and correlated to the potential-pH diagram. Freely corroding potential, passivation behaviour and pitting potential were examined as a function of a number of factors. These included the effects of different annealing and polishing pretreatments, the bulk solution pH and polarization methods. The corrosion potential (Ecorr) , pitting potential (Epit) and passivation behaviour were affected by the different pretreatments which changed the surface condition of GaAs. For mechanically polished samples, pitting corrosion was found in pH 7.0 solution only. The Ecorr and Eplt were independent of NO₃⁻ and Cl⁻ at pH 7.0. Initial polarization behaviour of p-GaAs at pH 2.0 and 12.0 followed the Tafel Law for semiconductors quite well. There was a reasonable correlation between the experimental observations and the potential-pH diagram of GaAs-H₂O system. SEM images of polarized samples showed that pits formed in NaCl and NaNO₃ had a different shape, being more elongated in NaCl. However, the walls of all pits appeared to be composed of {111} planes. In general, the pit distribution appeared to be similar to the dislocation distribution. A model of pitting corrosion of GaAs was proposed based on strain induced breakdown of the oxide film, localized changes in solution chemistry and the structure of the compound semiconductor.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

L'exposition de semi-conducteurs gaas de type p à un plasma radio fréquence d'hydrogène entraîne une diffusion d'hydrogène dans le matériau. L'analyse qualitative des profils de diffusion du deutérium conduit à la conclusion que l'hydrogène diffuse relativement librement dans les matériaux peu dopés et interagit fortement avec les accepteurs lorsque le taux de dopage est élevé. Ceci est valable aussi bien pour les accepteurs de la colonne 2 que pour ceux de la colonne 4. La diffusion de l'hydrogène dans les matériaux gaas dopés zinc, silicium et germanium entraîne une diminution de la concentration de trous libres et une augmentation de leur mobilité. Cette augmentation est le signe d'une neutralisation des accepteurs actifs par transformation de ces accepteurs en entités neutres. Le modèle proposé décrit ces entités neutres comme des complexes hydrogène dopants. Cet effet de neutralisation persiste lors de recuits thermiques jusqu'à des températures critiques dépendant de la nature de l'accepteur. La neutralisation la plus stable est obtenue dans le cas de gaas dope carbone. Par spectroscopie d'absorption infrarouge, nous avons mis en évidence des raies d'absorption associées au mode de vibration de l'hydrogène lie présent dans les complexes hydrogène accepteur. Nous avons montré que la structure microscopique des complexes dépendait du site de l'accepteur dans le réseau. Compte tenu que l'hydrogène diffusé sous une forme chargée positive, nous avons supposé que l'hydrogène introduisait un niveau donneur dans la bande interdite de gaas de type p et que le proton subissait des phénomènes de piégeages et de dé piégeages au cours de sa diffusion. A partir d'un modèle qui utilise ces hypothèses nous avons modélisé les profils de diffusion du deutérium dans gaas dope zinc. Nous avons montré, pour la première fois, que l'effet de neutralisation des accepteurs par l'hydrogène pouvait être utilisé pour réaliser des guides d'ondes optiques à base de gaas hydrogène. Les caractéristiques de ces guides d'ondes sont tout à fait encourageantes

Ce travail presente l'etude des dopants de type-p (be,c) pour l'epitaxie par jets moleculaires afin de fabriquer des transistors bipolaires a heterostructure gaas/ga#1#-#xal#xas tres performants. En ce qui concerne le dopant be, une etude des differents mecanismes de redistribution de l'impurete a ete entreprise. L'optimisation des parametres de croissance (temperature de croissance, rapport des flux v/iii, vitesse de croissance) a permis: 1) une augmentation de la longueur de diffusion des porteurs minoritaires dans la base associee a une amelioration de la qualite de la couche et 2) une importante minimisation de la diffusion du dopant durant des recuits a haute temperature (800c) apres croissance. Dans la seconde partie de ce travail, nous avons mis au point une cellule permettant d'evaporer du c a partir d'une source solide de graphite chauffee par effet joule direct. Des niveaux de dopages de type p jusqu'a 8 10#1#9 cm#-#3 ont ete obtenus. Cette etude a confirme le tres faible coefficient de diffusion du c comparativement aux impuretes conventionnelles ce type p (zn, be). Les proprietes de transport des porteurs minoritaires dans les couches dopees c epitaxiees par jets moleculaires classiques sont malgre tout restees tres faibles et n'ont pas permis d'obtenir dans l'etat actuel des composants performants. Nous pensons que ceci est du a la presence d'impuretes etrangeres, en particulier le fe, le cr et le cu dans la source de graphite, qui viennent s'incorporer dans la couche durant la croissance. Ces impuretes sont des centres profonds dans gaas. Des traitements specifiques de la source de graphite ont ete mis au point de facon a reduire la concentration de ces impuretes

ANALYSE DE LA PHOTOLUMINESCENCE DE STRUCTURES GaAs/(Ca,Sr))F2/GaAs, A FLUORURE ACCORDE EN MAILLE AU GAAS; INFLUENCE DES PARAMETRES DE CROISSANCE ET DE LA DISTANCE A L'INTERFACE. COMPARAISON DES PERFORMANCES DE SEMICONDUCTEUR HETEROEPITAXIE A CELLES DE GAAS EPITAXIE; ETUDE DE COUCHES DE GAAS EPITAXIE SUR CAF2 MASSIF

Modulation doped heterostructures have revolutionized the operation of field effect devices by increasing the speed of operation. One of the factors that affects the speed of operation of these devices is the mobility of the carriers, which is intrinsic to the material used. Mobility of electrons in silicon based devices has improved drastically over the years, reaching as high as 50.000cm2/Vs at 4.2K and 2600cm2/Vs at room temperature. However, the mobility of holes in p-type silicon devices still remains comparatively lesser than the electron mobility because of large effective masses and complicated valence band structure involved. Germanium is known to have the largest hole mobility of all the known semiconductors and is considered most suitable to fabricate high speed p-type devices. Moreover, it is also possible to integrate germanium and its alloy (Si1_zGex ) into the existing silicon technology. With the use of sophisticated growth techniques it has been possible to grow epitaxial layers of silicon and germanium on Si1_zGex alloy layers grown on silicon substrates. In tills thesis we investigate in detail the electrical properties of p-type germanium and n-type silicon thin films grown by these techniques. It is important to do a comparative study of transport in these two systems not only to understand the physics involved but also to study their compatibility in complementary field effect devices (cMODFET). The studies reported in this thesis lay emphasis both on the low and high field transport properties of these systems. We report experimental data for the maximum room temperature mobility of holes achieved m germanium thin films grown on Si1_zGex layers that is comparable to the mobility of electrons in silicon films. We also report experiments performed to study the high field degradation of carrier mobility due to "carrier heating" in these systems. We also report studies on the effect of lattice heating on mobility of carriers as a function of applied electric field. To understand the physics behind the observed phenomenon, we model our data based on the existing theories for low and high field transport. We report complete numerical calculations based on these theories to explain the observed qualitative difference in the transport properties of p-type germanium and ii-type silicon systems. The consistency between the experimental data and theoretical modeling reported in this work is very satisfactory.

>Magister Scientiae - MSc
This thesis starts with the reviewing of studies on the loading of noble metals and nanostructured metal oxides into bulk heterojunction organic solar cell device architectures. The reviews focused on the innovative developments in the use of various fullerene derivatives as electron acceptors in organic solar cells. It additionally reflected on the effect of metallic nanoparticles (NPs), such as gold (Au) and silver (Ag), on the performance of organic solar cells. Besides the metallic NPs, the effect of metal oxide nanoparticle loading, e.g. CuO, ZnO and TiO2, on the organic solar cell performance, and the use of noble metals doped TiO2 on the gas sensing application were reviewed.
2024

La mesure du taux de CO2 est un besoin relativement récent. Les travaux sur l'utilisation de nouveaux matériaux pour la réalisation de capteurs de gaz, efficaces et peu chers, suscitent des intérêts scientifique et technologique croissants. L'objectif de ces travaux de thèse est l'élaboration et la caractérisation de nouvelles couches sensibles obtenues par pulvérisation cathodique radiofréquence pour la réalisation de capteurs de CO2. Les films minces ont été déposés à partir d'une cible céramique de CuO, dans diverses conditions de dépôt, en variant la pression d'argon dans l'enceinte et la puissance RF appliquée. Dans un premier temps, nous avons caractérisé la structure et la microstructure des films bruts et recuits sous air par DRX, MEB, AFM et spectroscopie Raman. Nous avons également étudié les propriétés physiques des films minces ainsi que leur surface accessible par adsorption de gaz krypton (méthode de Brunauer, Emmett et Teller). Le traitement thermique à 450°C n'affecte pas la structure cristalline des couches, en revanche il tend à faire chuter fortement la surface accessible entre les colonnes. Après l'optimisation des paramètres de fonctionnement de la cellule de mesure, nous avons caractérisé les performances des films de CuO pour la détection du CO2. La meilleure réponse (?R/R=51 %) a été obtenue pour une couche élaborée à 2 Pa avec une puissance RF de 30W. De plus, la température optimale de mesure est relativement basse (T= 250°C). Le contrôle de la microstructure et plus particulièrement de la taille des grains s'est avéré être le paramètre principal qui impacte la réponse sous CO2. Les meilleurs résultats ont été obtenus avec des tailles de grains proches d'une vingtaine de nanomètres de diamètre. Une bonne modélisation de la réponse électrique en fonction de la taille des grains a pu être réalisée en prenant en compte un circuit électrique équivalent comportant une zone enrichie en porteur de type trous à la surface des grains et dont l'épaisseur est de l'ordre de la longueur de Debye
The measure of the rate of CO2 is a recent need. The works on the use of new materials for the conception of gas sensors based semiconductor oxides, effective and not expensive; arouse a huge interest in our society. The objective of this thesis is the elaboration and the characterization of new sensitive layers obtained by RF sputtering for the realization of the sensors of CO2. Thin films were deposited using two targets: CuFeO2 and CuO, under three conditions by varying argon pressure and RF power. First of all, the structure and the microstructure were studied for the as-deposited samples. Surface investigations carried out by Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Raman spectroscopy, BET measurements and MEB-FEG images have shown a strong influence of deposition technique parameters on film surface topography and morphology. In a second step, the thin films were annealed in air in order to oxidize the phase. For the composite CuO/CuFe2O4, Glow discharge optical emission spectrometry technique showed a structure in two layers stacked on top of each other for the thinner films. For the cupric films, no changes on both structure and microstructure have been revealed. Our films have then been evaluated for CO2 detection. The sensitive layers with different thicknesses were sensitive to 5000 ppm of CO2. The deposition parameters are optimized to obtain microstructure features which can enhance the sensitivity of the thin films as gas sensors. Best response was obtained for a cupric sample deposited in P2 30W conditions and was close to 50% at T = 250°C. We have demonstrates that cupric oxide alone can detect the CO2 gas and that the growth conditions determine the film surface characteristics. The gas sensing characteristics of these films are strongly influenced by both surface morphology and microstructure

Une etude theorique preliminaire a cette these a prevu que lorsque l'on introduit un gaz de trous bidimensionnel (2d) dans un puits quantique de semiconducteur semimagnetique, l'interaction entre les spins localises et les porteurs de charges induit une transition de phase ferromagnetique. Nous avons mis au point l'elaboration d'un tel systeme a base de tellurures en epitaxie par jets moleculaires, ainsi que la caracterisation au niveau microscopique des interfaces, du dopage et du transfert de porteurs dans le puits quantique. Ceci nous a permis d'elaborer des echantillons ayant donne lieu a toute une serie d'etudes physiques. Le dopage par modulation d'heterostructures de semiconducteurs ii-vi a base de tellure en epitaxie par jets moleculaires n'avait ete realise jusqu'a notre etude que pour un dopage de type n, sur des structures comportant du cdmgte comme materiau barriere, avec peu de magnesium. Or cet alliage est la clef de la realisation d'un bon confinement quantique dans les tellurures, surtout pour le dopage de type p ou la concentration en mg doit etre augmentee. L'utilisation d'une source d'azote ecr, dopant de type p, et l'optimisation des parametres de la croissance ont permis l'obtention d'un gaz de trous 2d de bonne densite, comme le montrent la spectroscopie optique, l'effet hall et la capacite-tension. L'etude de structures interdiffusees par sims, diffraction de rayon x et spectroscopie optique, nous a de plus permis de mieux comprendre les mecanismes de degradation en cours de croissance de nos couches comportant du magnesium, et dopees a l'azote. Un modele base sur la diffusion de l'azote a ete propose. Il a ensuite ete possible de realiser des structures semimagnetiques dans lesquelles l'interaction entre un gaz de trous 2d et des spins localises de manganese a permis la mise en evidence de la transition de phase ferromagnetique attendue theoriquement. Par ailleurs, un nouveau dopant de type n pour l'epitaxie par jets moleculaire des tellurures a ete teste avec succes sur des couches epaisses, ainsi que pour des heterostructures. Il s'agit de l'aluminium, dont le domaine d'utilisation est plus etendu que les autres dopants utilises jusqu'a present, puisqu'il permet d'obtenir une bonne efficacite meme sur des couches comportant du magnesium.

碩士
國立虎尾科技大學
光電與材料科技研究所
99
Zinc oxide (ZnO) is one of II-VI compound semiconductor with a wide band gap of 3.37 eV at room temperature and a large excition binding energy of 60meV, which makes it be an attractive material recently, especially in the application of blue and ultraviolet light-emitting diodes and laser. In this thesis, the ZnO film growth on gallium arsine (GaAs) substrate was prepared by double plasma-enhanced metal-organic chemical vapor deposition system (DPEMOCVD). Then, the as-grown ZnO film was treated with rapid thermal process by rapid thermal annealing. With the thermal energy, the arsenic atoms can diffuse into the ZnO film as a p-type dopant. Two subjects were investigated in this thesis, including annealing in oxygen and nitrogen ambient. The effects of annealing temperature and time related to the optoelectronic characteristics of ZnO film and surface structure were investigated in this thesis in oxygen and nitrogen. The experiment results indicated that under the condition of grows substrates temperature at annealing temperature of 425℃ and annealing time of 1 minute in nitrogen ambient, the hole concentration, carrier mobility, and resistivity is 2.38 × 1020 cm-3, 6.88 × 10-4 Ωcm, and 12.7 cm2/Vs, respectively. In other word, under the condition of grows substrates temperature at annealing temperature of 450℃ and annealing time of 1 minute in oxygen ambient, the hole concentration, carrier mobility, and resistivity is 3.07 × 1020 cm-3, 7.31 × 10-4 Ωcm , and 24.1 cm2/Vs, respectively.

碩士
義守大學
電子工程學系碩士班
94
Carbon doping in GaAs epilayers grown by metalorganic chemical vapor deposition (MOCVD) using CBr4 was successfully obtained . The growth rate decreased as CBr4 increased due to the etching effect of HBr caused by Br radicals. The growth rate increased while V/III ratio and TMGa flow rate increased. In addition, the growth rate increased with increasing the growth pressure and eventually saturated above 100 mbar. In the growth temperature rage of 500 to 650 °C, the growth rate decreased with increasing growth temperature. Carbon incorporation efficiency dependence on growth parameters was also investigated. The hole concentration was increasing with increasing CBr4 flow rate and eventually saturated at high flow rate. The hole concentration was also increasing with decreasing V/Ш ratio. This is because more carbon atoms can occupy As site on the growth surface under lower AsH3 flow rate. In addition, low growth temperature and high growth pressure can increase the carbon incorporation efficiency. Finally, we found the hole mobility decreased with increasing hole concentration due to the increasing of impurity scattering. The lattice mismatch of carbon-doped GaAs epilayers dependence on hole concentration was also described in detail. With increasing the hole concentration, the lattice mismatch of carbon-doped GaAs layers became large and all samples had the negative values. This is probably due to the covalent radius of C atoms is smaller than As atoms. While carbon atoms incorporate in the GaAs, the As sites will be occupied by carbon atoms on the growth surface and results in the decrease of the lattice constant.

碩士
中原大學
電子工程研究所
95
In this dissertation, we discussed the effects of the thickness of the Cu on the Ni/Pt/Cu/Au contact and of the individual Ni, Pt and Cu on the Ni/Pt/Cu/Ni/Au contact to p-GaAs in the beginning. Then, we sought for the optimum thickness of the Ni, Pt and Cu layers and the suitable annealing temperature and time for the lowest specific contact resistance ρc by transmission line method (TLM). As increasing the thickness of the Ni, Pt and Cu layers to 50nm, 50nm and 160nm, respectively, the lowest value (ρc �� 2.22×10-6 Ω-cm2) of specific contact resistance could be attained. Sequentially, we applied the optimum metallurgical structure of Ni (50nm) / Pt (50nm) / Cu (160nm) / Ni (40nm) / Au (50nm) layers as the positive electrode of the dual-junction (DJ) solar cells. Then, we measured these solar cells efficiency and compared the results with those of DJ solar cells having Ni (50nm) / Pt (80nm) / Au (200nm) p-type ohmic contact but without the copper metallurgical structure. We obtained the conversion efficiency about 17.19% for DJ solar cell with Ni (50nm) / Pt (50nm) / Cu (160nm) / Ni (40nm) / Au (50nm) and 17.39% for that with Ni (50nm) / Pt (80nm) / Au (200nm). In addition, we studied the thermal stability of these contact metals on the bulk GaAs and DJ solar cells. The ρc of Ni (50nm)/Pt (50nm)/Cu (160nm)/Ni (40nm)/Au (50nm) metallurgical structure is increased from 2.22×10-6 Ω-cm2 to 2.26×10-5 Ω-cm2 and the efficiency of DJ solar cell is decreased from 17.19% to 15.89% after annealing for 12 hours when held annealing temperature at 200oC in H2 ambient environment.

碩士
中原大學
電子工程研究所
96
In this dissertation, we discussed the effects of the thickness of the Ni and Pt on the Ni/Pt/Ag/Au ohmic contact metallurgical structure on p-GaAs in the beginning. We sought for the optimum thickness of the Ni and Pt layers and the suitable annealing temperature and time for the lowest specific contact resistance ρc by transmission line model method (TLM).We found out that the optimum metallurgical structure is Ni(25nm)/Pt(50nm)/Ag(300nm)/Au(20nm) which annealed at 300℃ for one minute. The lowest value (ρc=1.76×10-6 Ω-cm2) of specific contact resistance could be attained. And then, we used the same method to seek for the optimum thickness of the Ni layer and the suitable annealing temperature and time for the lowest specific contact resistance ρc. We found out that the optimum metallurgical structure is Ni(25nm)/ Ag(300nm)/Au(20nm). The lowest specific contact resistance value (ρc=1.2×10-6 Ω-cm2) could be attained. The sample annealed at 300℃ for one minute. 　　In addition, we studied the thermal stability of these ohmic contact metallurgical structures on the bulk GaAs. The ρc of these ohmic contact metallurgical structures were increased five to ten times after annealing for 4 to 60 hours when held annealing temperature at 200℃ in H2 ambient environment. 　　Sequentially, we applied the optimum ohmic contact metallurgical structure Ni (25nm) / Ag (300nm) / Au (20nm) as the positive electrode of the dual-junction (DJ) solar cells. Then, we measured the efficiency (Eff), fill factor (FF), open circuit voltage (Voc) and short circuit current (Isc) of solar cells. As the result of the optimum ohmic contact condition, all the parameters of solar cell had the best performance at the optimum ohmic contact condition.

碩士
中原大學
電子工程研究所
99
Abstract In this dissertation, we discussed the effects of thickness Pd on the Pd / Au and Pd / Ag / Au ohmic contact metallurgical structure deposited on P-Ge material. At first ,we studied the optimum thickness of the Pd layer and the suitable annealing temperature and time for obtaining the lowest specific contact resistance ρc on P-Ge by transmission line model method (TLM).We found out that the optimum metallurgical structure is Pd (30 nm) / Au (60 nm) after annealed at 350 ℃ for 2 minutes. The lowest value ρc=6×10-6 Ω-cm2 of specific contact resistance could be attained. Then, we used the same method to study the optimum thickness of the Pd、Ag and Au layers and the suitable annealing temperature and time for the lowest specific contact resistance ρc. We found out that the optimum metallurgical structure is Pd (20 nm) / Ag (60 nm) / Au (20 nm), in which the lowest specific contact resistance value ρc=3.9×10-5 Ω-cm2 could be attained when the sample is annealed at 350℃ for 2 minutes. Then, we applied the optimum ohmic contact metallurgical structure Pd (30 nm) /Au (60 nm) and Pd (20 nm) / Ag (60 nm) / Au (20nm), respectively, as the p-type ohmic contact of dual-junction (DJ) solar cells. After that, we measured the efficiency (Eff), fill factor (FF), open circuit voltage (Voc) and short circuit current (Isc) of solar cells. The measured results indicate that solar cells had the best performance when having the ohmic contact fabricated at the optimum conditions.

碩士
國立臺南大學
材料科學系碩士班
106
This study is divided into two parts. The first part is the study of the effect of furnace annealing and rapid thermal annealing (RTA) temperature on the structure and optical properties of arsenic-doped zinc oxide (ZnO:As) film on GaAs substrates. The results show that the samples with both furnace annealing and rapid thermal annealing have better film quality including reduction of the residual stress of the film and the formation of high p-type conductivity. Although the hole concentration of the sample with RTA 600 oC is as high as 1019 cm-3, the defects such as AsZn-2VZn complex are formed leading to relatively higher roughness and poor optical emission. Furnace annealing 500 oC and rapid thermal annealing 550 oC are superior condition for better quality of p-type ZnO: As thin film. The second part is the study of the effect of crystal growth time and manganese precursor temperature on the cadmium manganese telluride (Cd1-xMnxTe) film grown on silicon (Si) substrates. The results show that higher doping concentration of manganese (Mn) is achieved in Cd1-xMnxTe for crystal growth time 6-hours. Manganese doping can help to reduce defects of Te-Te bond of the Cd1-xMnxTe film. Better crystalline structure, lower surface roughness and larger blue shifts of luminescence wavelength are realized when the precursor temperature of Mn is raised. For the precursor temperature of Mn at 820 °C, the luminescence wavelength can shift to 629 nm and has relatively low defect density of Te-Te bond. Cd1-xMnxTe is a suitable material as an intermediate energy gap material in the applications of Si-based solar cell.

Increased interest in the field of sensor technology stems from the availability of an inexpensive and robust sensor to detect and quantify the presence of a specific gas. Bulk p-CuO/n-ZnO heterocontact based gas sensors have been shown to exhibit the necessary sensitivity and selectivity characteristics, however, low interfacial CuO/ZnO contact area and poor CuO/ZnO connectivity limits their effective use as gas sensors. The phase equilibria between CuO and ZnO exhibits limited solubility. By exploiting this concept, a CuO/ZnO mixed solution is formed by combining CuO and ZnO precursors using wet chemical (sol-gel) techniques. Thin films fabricated using this mixed solution exhibit a unique CuO/ZnO microstructure such that ZnO grains are surrounded by a network of CuO grains. This is highly beneficial in gas sensing applications since the CuO/ZnO heterostructure interfacial area is considerably increased and is expected to enhance sensing characteristics. This work builds on previous research by Dandeneau et al. (Thin film chemical sensors based on p-CuO/n-ZnO heterocontacts, Thin Solid Films, 2008). CuO/ZnO mixed solution thin films are fabricated using the sol-gel technique and subsequently characterized. X-ray diffraction (XRD) data confirms the phase separation between ZnO and CuO grains. Scanning electron microscopy (SEM) as well as energy dispersive spectroscopy (EDS) reveal a network of ZnO grains amidst a matrix of CuO grains. Optical and electrical characterization provide material parameters used to construct an energy band diagram for the CuO/ZnO heterostructure. Aluminum interdigitated electrodes (IDEs) are patterned on the thin film and gas sensing characteristics in the presence of oxygen and hydrogen are investigated. Optimization of the electrode geometry is explored with the aim of increasing the sensitivity of the sensor in the presence of hydrogen gas.
Graduation date: 2010