This thesis is about the growth of ZnO thin films for optoelectronic applications. ZnO thin films were grown using plasma assisted molecular beam epitaxy and were studied using various conventional and novel characterisation techniques. The significance of different growth variables on growth efficiency was investigated. The growth rate of ZnO films was found to be linearly dependent on the Zn flux under O-rich growth conditions. Under Zn-rich conditions, the growth rate was dependent on both atomic and molecular oxygen flux. By characterising the oxygen plasma generated using different RF power and aperture plate designs and correlating the results with the growth rates observed, it was found that atomic oxygen was the dominant growth species under all conditions. Molecular oxygen also participated in the growth process, with its importance dependent on the aperture plate design. In addition, an increase in growth temperature was found to monotonically decrease the growth rate. A growth rate of 1.4 Å/s was achieved at a growth temperature of 650 ℃ by using an oxygen flow rate of 1.6 standard cubic centimetres utilising a plasma source with a 276 hole plate operating at 400 W, and a Zn flux 1.4✕10¹⁵ atoms/cm²⋅s. Characterisation of the MBE grown thin films revealed that the qualities of ZnO thin films were dependent on the growth conditions. Experimental evidence suggested that a maximum adatom diffusion rate can be achieved under Zn-rich conditions, giving samples with the best structural quality. O-rich conditions in general led to statistical roughening which resulted in rough and irregular film surfaces. Experimental results also suggested that by increasing the atomic oxygen content and decreasing the ion content of the plasma, the excitonic emission of the ZnO thin films can possibly be improved. It was also found that the conductivity of the films can possibly be reduced by increasing the plasma ion content. By investigating the evolution of the buffer layer surface during the early stages of growth, dislocation nucleation and surface roughening were found to be important strain relief mechanisms in MBE grown ZnO thin films that affected the crystal quality. The usage of LT-buffer layers was found to improve substrate wetting, and was shown to significantly reduce dislocation propagation. Further strain reduction was achieved via the application of a 1 nm MgO buffer layer, and a significant reduction of carrier concentration and improvement in optical quality was subsequently observed. A carrier concentration of <1✕10¹⁶ cm⁻³ and a near band emission full width half maximum of 2 meV was observed for the best sample. The study of electrical characteristics using the variable magnetic field Hall effect confirmed the existence of a degenerate carrier and a bulk carrier in most MBE grown ZnO thin films. The bulk carrier mobility was measured to be ~120 - 150 cm²/Vs for most as-grown samples, comparable to the best reported value. A typical bulk carrier concentration of ~1✕10¹⁶ - 1✕10¹⁸ cm⁻³ was observed for as-grown samples. Annealing was found to increase the mobility of the bulk carrier to ~120 - 225 cm²/Vs and decrease the bulk carrier concentration by two orders of magnitude. Using time resolved photoluminescence, it was found that the radiative recombination in MBE grown ZnO thin films was dominated by excitonic processes, and followed a T³⁄² trend with temperature. A maximum radiative lifetime of 10 ns was observed for as-grown samples. The non-radiative lifetime in ZnO thin films was dominated by the Shockley-Read-Hall recombination processes. The modelling of the temperature dependence of the non-radiative lifetime suggested that an electron trap at ~0.065 eV and a hole trap at ~0.1 eV may be present in these samples. The application of time resolved photoluminescence also allowed the direct observation of carrier freeze-out in these ZnO films at low temperature.

This thesis concerns new hydrogen- and polarity-related effects in the photoluminescence of ZnO single crystal wafers and the relationship between surface electron accumulation and surface hydroxyl coverage on different ZnO surfaces. A comparative study of the low temperature photoluminescence of various types of hydrothermal and melt-grown ZnO wafers revealed several new hydrogen-related exciton recombination lines and a number of consistent polarity-related differences in the PL emission from different crystallographic surfaces. Temperature-dependent PL measurements were extensively used to distinguish the ground and excited state transitions involved in these effects. ZnO samples of different surface polarity were annealed in oxygen and nitrogen gases and in hydrogen-containing forming gas mixtures in an attempt to identify the origin of these new PL features. The well known aluminium-related I_₆ recombination line was resolved into two separate features in hydrothermal ZnO, and the new component I6-H (3.36081 eV) was found to repeatedly quench and then re-emerge after annealing in oxygen and forming gas, respectively. A model involving an aluminium - lithium - hydrogen defect complex was proposed for I6-H and further tested via hydrogen and deuterium implantation experiments on hydrothermal ZnO wafers with different lithium concentrations. These experiments also provided evidence for the involvement of a different lithium-hydrogen defect complex in other hydrogen-related emission lines I₄b,c (3.36219 eV and 3.36237 eV) unique to hydrothermal ZnO. In addition, a broad Gaussian-shaped feature observed in the near-band-edge PL emission from the O-polar (000‾1), a-plane (11‾20) and r-plane (1‾102) faces of ZnO was shown to be surface sensitive and also related to hydrogen. The involvement of hydrogen in the chemical and electronic properties of different ZnO surfaces was also investigated. The thermal stability of the hydroxyl termination and the associated downward surface band bending on the polar and non-polar surfaces of ZnO was studied by synchrotron and real-time photoelectron spectroscopy, both during and after annealing and subsequent H₂O/H₂ dosing in ultra-high vacuum conditions. On the O-polar face, the band bending could be reversibly switched over a range of approximately 0.8 eV by adjusting the surface H-coverage using simple UHV heat treatments and atmospheric exposure. A transition from electron accumulation to electron depletion on the O-polar face was observed at a H-coverage of approximately 0.9 monolayers. In contrast, the downward band bending on the Zn-polar face was significantly more resilient and electron-depleted surfaces could not be prepared by heat treatment alone. This was also the case for in situ cleaving in UHV conditions which failed to produce hydroxyl-free surfaces due to migration of hydrogen from the bulk to the cleaved surface. Interestingly, the thermal stability of the hydroxyl termination on the a-plane (11‾20) and m-plane (10‾10) surfaces was signiifcantly lower than on the polar faces due to the availability of a lower energy desorption pathway and the electrostatic stability of these non-polar surfaces in their clean, bulk terminated form. The surface band bending on the non-polar ZnO surfaces was also found to be directly related to their OH coverage with a transition from downward to upward band bending, similar to that observed on the O-polar face, as the OH coverage was reduced. Thermal admittance spectroscopy and deep level transient spectroscopy was used to investigate the effect of lithium removal on the defect nature of hydrothermal ZnO. A number of new defects were introduced by the high temperature (1100-1400°C) annealing/re-polishing process used to reduce the lithium concentration, particularly E₁₉₀ (also known as T2) which is thought to be related to Zn vacancies. Significantly, both the E₅₀ defect level and the I6-H PL emission line were absent after lithium (and hydrogen) removal suggesting an association of both these features with the same aluminium - lithium - hydrogen defect complex.

Il est couramment admis que le niveau de pollution dans l'environnement intérieur pouvait dépasser le niveau de pollution extérieur. C'est la raison pour laquelle la qualité de l'air intérieur est devenue une préoccupation sociétale importante en raison de la durée croissante que nous passons dans ces environnements. Les procédés d'oxydation avancée (POA), parmi lesquels l'oxydation photocatalytique, sont des techniques pertinentes pour la purification de l'air. En photocatalyse, les nanotubes de titane montrent un intérêt tout particulier en raison de leurs propriétés intrinsèques spécifiques de par leurstructure tubulaire. Ce matériau unidimensionnel engendre un rapport surface/volume important qui donne accès à une surface spécifique et à des capacités d'adsorption importantes, mais aussi à des propriétés de transport électronique accrues. Deux molécules modèles gazeuses ont été retenues, la méthyléthylcétone (MEC) et le sulfure de dihydrogène (H2S). Ces molécules diffèrent de par leur composition chimique (présence ou non d'hétéroatomes) et leurs propriétés physico-chimiques et reflètent différentes catégories de pollutions chimiques et olfactives. Afin d'améliorer les performances photocatalytiques des nanotubes, de TiO2 synthétisés par méthode hydrothermale, que ce soit sous illumination UV-A ou solaire, des modifications avec un autre semi-conducteur WO3 ou ZnO ont été entreprises. Les mêmes modifications ont également été réalisées sur le photocatalyseur commercial TiO2 P25 (Evonik). Une des finalités de ce travail est la corrélation des conditions de synthèse de ces matériaux avec leurs caractéristiques physico-chimiques et avec leurs propriétés photocatalytiques vis-àvis de l'élimination des deux polluants étudiés. Une approche mécanistique a également été menée.

Dans cette thèse, nous avons étudié les propriétés expérimentales des polaritons unidimensionnels dans les microfils de ZnO dans le but d'étudier le régime de dégénérescence quantique des polaritons à haute température et en régime de confinement de basse dimensionnalité. ZnO est en effet un matériau semiconducteur à grand gap dans lequel l'exciton bénéficie d'une très forte énergie de liaison qui garantit leur stabilité à température ambiante. D'autre part, la géométrie en "fil" de section hexagonale et de diamètre micrométrique confine les modes photoniques et les rend unidimensionnels. On montre que l'interaction entre l'exciton et ces modes photoniques est en régime de couplage fort, et que les polariton-excitoniques qui en résultent sont eux aussi en régime de confinement unidimensionnel. Cette thèse propose une étude détaillée de la physique de ces polaritons 1D. Dans un premier temps, on démontre que le régime de couplage fort unidimensionnel est conservé jusqu'à température ambiante avec une très grande énergie de Rabi de 300 meV pour une largeur de raie typique 75 fois plus faible. Cette faible largeur de raie, même à température ambiante, est une conséquence inattendue de la grande énergie de Rabi en comparaison de l'énergie maximum des phonons dans ZnO. Cet effet isole très efficacement les polaritons des vibrations thermiques du réseau. Nous nous sommes intéressés aussi à une structure similaire: les microfils de GaN. Dans ces fils, on profite d'une zone fortement dopée pour comparer expérimentalement le spectre en régime de couplage faible et en régime de couplage fort dans le même fil. Nous avons ensuite étudié les propriétés des gaz de polaritons dans les microfils de ZnO sous forte excitation dans le but d'atteindre le régime de dégénérescence quantique 1D. Nous démontrons qu'un régime de laser à polaritons est atteint à basse température en régime de couplage fort dans une situation inédite où les polaritons sont à 97% excitoniques. Cette propriété est comprise grâce à une étude détaillée des propriétés de relaxation des excitons vers les états de polaritons en régime de faible et forte excitations. Cette thèse donne les bases de la compréhension des polaritons unidimensionnels dans les microfils de ZnO. Les propriétés observées montrent que les microfils de ZnO sont particulièrement adaptés à l'étude des gaz de polaritons dégénérés 1D à haute température.

L'oxyde de zinc (ZnO) est un semi-conducteur à large gap direct (3,37 eV) qui possède de nombreuses propriétés intéressantes (piézoélectrique, optique, catalytique, chimique...). Un large champs d'applications fait de lui l'un des matériaux les plus étudiés de la dernière décennie, notamment sous forme nanostructurée. Dans ce travail, nous nous intéressons à la synthèse par électrochimie des couches minces, des micro- & nano-plots, et des nanofils de ZnO. Deux méthodes ont été utilisées : la première dite Template consiste à la fabrication des micro- et nanopores en réseau ordonné à l'aide de la technique lithographique dans lesquels a lieu la croissance du ZnO ; la seconde consiste à la croissance libre de réseau de nanofils. Les caractérisations structurales, morphologiques et optiques du ZnO ainsi élaboré ont été réalisées par diffractométrie des rayons-X (DRX), microscopie électronique à balayage (MEB), microscopie électronique en transmission (MET), spectroscopie Raman, spectroscopie UV et photoluminescence (PL). Les propriétés électriques des couches minces et des réseaux de nanofils (sous l'effet collectif) de ZnO ont été étudiées par des mesures "courant tension" (I-V) à température ambiante dans la configuration métal/semi-conducteur/métal à l'aide d'un réseau de micro-électrodes métalliques déposé en surface du ZnO. Cette étude nous a permis de déterminer qualitativement la conductivité électrique du ZnO et les différents paramètres de la jonction Schottky entre le ZnO et le substrat doré. Celle-ci est fondamentale et indispensable pour la réalisation d'un dispositif de récupération d'énergie tel que le nanogénérateur de courant piézoélectrique à base de nanofils de ZnO

Applications of zinc oxide (ZnO) for optoelectronic devices, including light emitting diodes, semiconductor lasers, and solar cells have not yet been realized due to the lack of high-quality p-type ZnO. In the research presented herein, pulsed laser deposition is employed to grow Ag-doped ZnO thin films, which are characterized in an attempt to understand the ability of Ag to act as a p-type dopant. By correlating the effects of the substrate temperature, oxygen pressure, and laser energy on the electrical and microstructural properties of Ag-doped ZnO films grown on c-cut sapphire substrates, p-type conductivity is achieved under elevated substrate temperatures. Characteristic stacking fault features have been continuously observed by transmission electron microscopy in all of the p-type films. Photoluminescence studies on n-type and p-type Ag-doped ZnO thin films demonstrate the role of stacking faults in determining the conductivity of the films. Exciton emission attributed to basal plane stacking faults suggests that the acceptor impurities are localized nearby the stacking faults in the n-type films. The photoluminescence investigation provides a correlation between microstructural characteristics and electrical properties of Ag- doped ZnO thin films; a link that enables further understanding of the doping nature of Ag impurities in ZnO. Under optimized deposition conditions, various substrates are investigated as potential candidates for ZnO thin film growth, including r -cut sapphire, quartz, and amorphous glass. Electrical results indicated that despite narrow conditions for obtaining p-type conductivity at a given substrate temperature, flexibility in substrate choice enables improved electrical properties. In parallel, N+-ion implantation at elevated temperatures is explored as an alternative approach to achieve p-type ZnO. The ion implantation fluence and temperature have been optimized to achieve p-type conductivity. Transmission electron microscopy reveals that characteristic stacking fault features are present throughout the p-type films, however in n-type N-doped films high-density defect clusters are observed. These results suggest that the temperature under which ion implantation is performed plays a critical role in determining the amount of dynamic defect re- combination that can take place, as well as defect cluster formation processes. Ion implantation at elevated temperatures is shown to be an effective method to introduce increased concentrations of p-type N dopants while reducing the amount of stable post-implantation disorder. Finally, the fabrication and properties of p-type Ag-doped ZnO/n-type ZnO and p-type N-doped ZnO/n-type ZnO thin film junctions were reported. For the N-doped sample, a rectifying behavior was observed in the I-V curve, consistent with N-doped ZnO being p-type and forming a p-n junction. The turn-on voltage of the device was ∼2.3 V under forward bias. The Ag-doped samples did not result in rectifying behavior as a result of conversion of the p-type layer to n-type behavior under the n- type layer deposition conditions. The systematic studies in this dissertation provide possible routes to grow p-type Ag-doped ZnO films and in-situ thermal activation of N-implanted dopant ions, to overcome the growth temperature limits, and to push one step closer to the future integration of ZnO-based devices.

As the science and technology advance, people are looking for new discoveries to solve the existing problems and improve the quality of life. In this processes of development, nanoscience and nanotechnology have attracted technologists' attention and turned out to be one of the most promising technologies that could have a revolutionary impact. Znic Oxide (ZnO) nanostructures, in particular nanowires (NWs), have the potential to be one of such revolutionary material. ZnO is a piezoelectric, transparent and semiconducting material. With a direct band gap of 3.37eV and large excitation binding energy (60meV), ZnO exhibits near-UV emission, and transparent conductivity. ZnO NWs, with all of the properties of bulk ZnO, have other properties that are distinct to nanoscale material. All of these make ZnO NWs a very unique material that has many potential applications in system miniaturization. System-on-package (SOP) technology is a new concept developed to solve the integration problem in microelectronic industry. SOP technology paradigm provides system-level miniaturization in a package size that makes today's hand-held devices into multi-functional systems, with applications ranging from computing, wireless communications, health care to personal security. The SOP is a system miniaturization technology that ultimately integrates nanoscale thin film components for batteries, thermal structures, active and passive components in low cost organic packaging substrates, leading to micro to nanoscale modules and systems. The goal of this research is to investigate and utilize the unique properties of ZnO NWs and apply them to the fabrication of devices that can be integrated with SOP platform. The issues include developing techniques to manipulate and align ZnO NWs; developing contact preparation method to improve the contact conductance for the fabrication of ZnO NW based devices. Also, the investigation of the oxygen diffusion coefficient in ZnO NWs is carried out, which serves as the basis of ZnO NWs for sensing applications. Two practical applications, which include fabricating and characterizing SOP compatible ZnO NW based bio-sensor and SOP compatible ZnO NW based nano-generator, are evaluated. Finally the remaining work beyond the scope of the thesis is outlined.

ZnO thin films and nanostructures were grown by eclipse pulsed laser deposition (EPLD) for the first time. On bare sapphire held at 600 °C, a complex nanostructured surface was formed when ablating a metallic Zn target in an oxygen ambient. Nanorods grown by a vapor-solid mechanism clumped together in well separated, micron-sized regions. Nanoscale pyramids with 6 fold symmetry formed between the nanorod clumps by vapor-liquid-solid growth. Strong photoluminescence (PL) was observed from the EPLD grown samples, an order of magnitude stronger than PLD grown nanorods formed under similar growth conditions. Low temperature PL was dominated by the I₇ exciton, which still has an unknown origin. Excitation intensity dependence of I₇ was drastically different than the rest of the nearby excitonic features, behavior which has not been previously reported for bound excitons in ZnO. I₇ also showed large, seemingly random variations in intensity across the surface of each sample compared to the other nearby recombinations, suggesting a structural connection. Introduction of a buffer layer had a profound effect on the morphology and PL from EPLD grown ZnO from a metallic Zn target. Pt has a high melting temperature, which helped suppress the vapor-liquid-solid nanostructure growth resulting in thin-film formation. For standard PLD, the ZnO film showed large grains separated by cracks on the surface. Due to the reduced growth rate in the EPLD geometry, the ZnO layer had a high density of nanoscale pores, reminiscent of the porous Pt buffer layer. Strong PL emission, which was dominated by I₇, was observed from the ZnO/Pt/Al₂O₃ which showed unusual blue/violet emission when the EPLD geometry was used for growth. Thin ZnO buffer layers deposited at reduced temperature also had a profound effect on EPLD grown ZnO, resulting in a random array of nanorods with alignment which was dependent on the growth temperature of the buffer layer. Buffer layers offer another dimension in the control over epitaxial structures and show large potential for EPLD growth of ZnO. Pb was the dominant impurity in the Zn targets used for EPLD growth, hinting at a Pb-related origin for the I7 peak. To explore this idea, hydrothermally grown bulk ZnO was ion-implanted with Pb and then annealed in oxygen at 600 °C to repair damage to the crystal. PL emission intensity was substantially reduced in the Pb-implanted ZnO but the line widths were preserved. No evidence of an I₇ feature was seen for Pb concentrations of up to 0.10%, three orders of magnitude higher than the expected level in the EPLD grown ZnO. However, this does not rule out a Pb-related complex as the origin of I₇ since Pb has complicated interactions with the impurities and native defects in ZnO. Instead of I₇, other sharp excitonic features were observed near the band edge. A bound exciton with a localization energy of 12.4 ± 0.2 meV was observed in the Pb-implanted samples and was attributed to neutral interstitial Pb donors. Pb-implantation produced a clear PL signature which is unique enough to unambiguously detect its presence in ZnO. EPLD also proved successful at depositing oxides of the noble metals. Ir, Pt, Pd, and Ru targets were ablated in oxygen and argon ambients and films were collected on room temperature substrates. Growth in argon resulted in pure metal while oxidized layers were obtained in oxygen. This was clearly evident by the semiconductor-like transmission spectra observed for the oxidized samples. The high fluence used for these growths promoted the oxidation of these resilient metals while the shadow mask blocked most of the molten particulates generated by the high fluence. EPLD is an excellent way to produce oxides from metallic targets, a technique which should be explored in more detail for many material systems.

Orientador: Victor Ciro Solano Reynoso / Banca: Cláudio Luiz Carvalho / Banca: Celso Xavier Cardoso / Resumo: Neste trabalho foram depositados em substrato vítreo, filmes finos de Óxido de Zinco puro (ZnO) e dopados com alumínio (ZnO:Al) e manganês (ZnO:Mn), utilizando a técnica spray-pirólise. Foram investigadas as propriedades estruturais, ópticas e elétricas dos filmes, assim como, a dependência com a temperatura de deposição e concentração. As temperaturas utilizadas para deposição dos filmes finos foram 400 ºC e 450 ºC, e a concentração de dopantes variaram de 1 a 5 átomo por cento (at%). As técnicas de difração de raios-X e espectroscopia por refletância no infravermelho foram utilizadas para avaliar as características estruturais dos filmes. A Espectroscopia de transmitância na região do UV-Vis foi utilizada como uma das técnicas no estudo das propriedades ópticas, fornecendo valores da banda proibida. A técnica do ângulo de Brewster, foi utilizada com o intuito de avaliar o índice de refração e a espessura dos filmes finos. A avaliação da resistividade foi realizada com a finalidade de estudar a propriedade elétrica, e medidas do efeito Hall para investigar a densidade dos portadores de carga e mobilidade dos filmes semicondutores. A análise dos difratogramas de raio-X, revela picos de difração típicos de uma estrutura policristalina tipo wurtzita. As medidas de refletância especular por FTIR identificam ligações de estiramento do Zn-O na região de 450 cm-1. A técnica do ângulo de Brewster fornece resultados das espessuras dos filmes finos na faixa de 150 a 240 nm. As medidas de espectroscopia de transmitância na região UV-vis é avaliada em torno de 85%. Com os resultados da espessura dos filmes pelo ângulo de Brewster e medidas de transmitância foi calculado na região de forte absorção o coeficiente de absorção destes filmes. O valor do coeficiente de absorção é um parâmetro fundamental para determinação da banda de energia proibida... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work were deposited in glass substrate, thin films of pure zinc oxide (ZnO) and doped with aluminum (ZnO: Al) and manganese (ZnO: Mn) used the spray-pyrolysis technique. The structural, electrical and optical properties of thin films were investigated in dependence the concentration and temperatures deposition. The thin films temperatures deposition were 400 °C and 450 º C, and the doping concentration were from 1 at% to 5 at% range. The deposition technique used aims to obtain good adhesion to the substrate and uniformity of the films. The X-ray diffraction spectroscopy and infrared reflectance were used to evaluate the structural characteristics of the films. The UV-Vis transmittance spectroscopy was used in the study of optical properties, providing values of band gap. The other technique for this purpose is the Brewster angle technique in order to evaluate the refractive index and thickness of thin films deposited on a glass substrate. The resistivity and Hall Effect measurements were used for to investigate the charge carriers density and mobility in semiconductor films. The analysis of the X-ray diffraction shows typical peaks of polycrystalline wurtzite structure. Measurements the FTIR specular reflectances identify bond stretching of Zn-O in the region of 450 cm-1. The Brewster angle technique provides results the thin films thickness in the 150 to 240 nm range. The thin films UV/VIS transmittance measurements are valued around 85%. With the results of the thin film thickness by Brewster angle and measures transmittance were calculated the absorption coefficient data values in strong absorption region. The absorption coefficient is an important parameter for determination the band gap energy. These values, for the ZnO semiconductor is in 3.2 eV range. The resistivity's measurements by Van der Pauw method showed the resistivity of ZnO thin films doped with... (Complete abstract click electronic access below) / Mestre

abstract: Transparent conductive oxides (TCOs) are used as electrodes for a number of optoelectronic devices including solar cells. Because of its superior transparent and conductive properties, indium (In) tin (Sn) oxide (ITO) has long been at the forefront for TCO research activities and high-volume product applications. However, given the limited supply of In and potential toxicity of Sn-based compounds, attention has shifted to alternative TCOs like ZnO doped with group-III elements such as Ga and Al. Employing a variety of deposition techniques, many research groups are striving to achieve resistivities below 1E-4 ohm-cm with transmittance approaching the theoretical limit over a wide spectral range. In this work, Ga-doped ZnO is deposited using pulsed laser deposition (PLD). Material properties of the films are characterized using a number of techniques. For deposition in oxygen at pressures >1 mTorr, post-deposition annealing in forming gas (FG) is required to improve conductivity. At these higher oxygen pressures, thermodynamic analysis coupled with a study using the Hall effect measurements and photoluminescence spectroscopy suggest that conductivity is limited by oxygen-related acceptor-like defects in the grains that compensate donors, effectively reducing the net carrier concentration and creating scattering centers that reduce electron mobility. Oxygen is also responsible for further suppression of conductivity by forming insulative metal oxide regions at the grain edges and oxygen-related electron traps at the grain boundaries. The hydrogen component in the FG is thought to passivate the intra-grain acceptor-like defects and improve carrier transport across these grain boundaries. Given this deleterious effect of oxygen on conductivity, depositions are performed in pure argon (Ar), i.e., the only oxygen species in the growth ambient are those ejected directly from the PLD solid source target. Ga-doped ZnO deposited in Ar at 200 °C and 10 mTorr have resistivities of 1.8E-4 ohm-cm without the need for post deposition annealing. Average transmittance of the Ga-doped films is 93% over the visible and near infrared (IR) spectral regions, but free carrier absorption is a limiting factor further into the IR. After annealing in FG at 500 °C, a 300 nm Ar film has a Haacke figure of merit of 6.61E-2 sq. ohm. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2011