xv, 132 p. : ill. A print copy of this title is available from the UO Libraries, under the call number: SCIENCE TK7871.15.F5 H325 2007 / The effects of sulfur alloying on the electronic properties of CuIn(SeS) 2 and CuInGa(SeS) 2 materials has been investigated using sophisticated junction capacitance techniques including drive-level capacitance profiling and transient photocapacitance and photocurrent spectroscopies. CISSe and CIGSSe materials are used as absorber layers in thin-film photovoltaic devices. By characterizing the electronic properties of these materials we hope to understand how these materials can be improved to make thin-film devices with better conversion efficiencies. Sulfur widens the bandgap of these materials by moving the valence band to lower energies and the conduction band to higher energies. This significantly affects the electronic structure of these devices by increasing the activation energies of dominant acceptor levels and lowering room temperature free hole carrier densities. Using optical spectroscopies we observe a large, broad defect that also changes its apparent energetic depth with sulfur alloying. The occupation of this defect was controlled both optically and thermally, and showed a striking temperature dependence. This temperature dependence was measured by recording the relative defect signal, the ratio of the TPC signal in the defect regime to the above bandgap regime, as a function of temperature. As the temperature of the measurement was decreased, steps in the relative defect signal were observed, indicating the turning off of the thermal pathway that emptied trapped charge from the defect. Remarkably, such steps were seen at the same temperature in CISSe and CIGSSe devices with similar sulfur content. In addition, no steps were seen in CMS devices. This points to a defect state specific to the incorporation of sulfur in the absorber material. We hope that a better understanding of the electronic structure of these materials will assist in the creation of improved wide-bandgap thin-film photovoltaic devices. / Adviser: J. David Cohen

Une des propriétés intrinsèques des matériaux diélectriques est d'accumuler des charges électriques sous l'action de contraintes extérieures (température, champ électrique...). Ce phénomène utile dans certaines applications (mémoires non volatiles...), demeure en général une cause de défaillance (microsystèmes...). Il convient donc de disposer d'une méthode permettant de mesurer cette densité de charges aux échelles pertinentes pour le système. Du fait de la miniaturisation, les méthodes classiques de mesure de charge d'espace (PEA, FLIMM,...) ne sont plus adaptées, car leurs résolutions latérales de quelques micromètres est bien supérieure aux dimensions nanométriques des systèmes. Une nouvelle méthode de mesure de la charge d'espace basée sur la microscopie à champ proche, et plus particulièrement la mesure de potentiel de surface par microscopie à sonde de Kelvin (KPFM), permet d'obtenir des informations sur l'état de charge du matériau avec une résolution nanométrique. Notre objectif est d'étudier les phénomènes d'injection et de rétention de charges dans des diélectriques minces. Pour cela deux voies ont été explorées. La première consiste à injecter localement des charges à la surface d'une couche mince de SiOxNy d'épaisseur variable (entre 6nm et 130nm) et à mesurer les modifications du potentiel de surface induit par les charges. Les mesures de potentiel de surface (KPFM) et de courant (C-AFM) couplées à des simulations du champ électrique par éléments finis (COMSOL) ont mis en évidence que deux mécanismes sont en jeu lors de l'injection de charges : le piégeage dans la couche et la conduction au travers de la couche. Pour les épaisseurs les plus fines la conduction est le mécanisme majoritaire (ce qui limite la quantité de charges piégées) alors que pour les films plus épais le piégeage est majoritaire. Pour les films d'épaisseur intermédiaire les deux mécanismes sont en compétition. Une fois les charges injectées leur dissipation se fait majoritairement dans le volume selon une dynamique indépendante de l'épaisseur de la couche. La seconde voie consiste à étudier l'injection et le déplacement de charges entre deux électrodes latérales enfouies dans le diélectrique. Cette structure permet de s'affranchir du manque de sensibilité de la mesure KPFM à la profondeur des charges dans le volume et d'étudier les phénomènes d'injection aux interfaces et le transport de charges sous champ électrique. Le champ électrique induit entre les deux électrodes polarisées a été simulé par éléments finis sous COMSOL et comparé aux mesures de potentiel KPFM. Nous avons ainsi pu caractériser l'injection à l'interface métal/diélectrique et nous avons montré la faisabilité d'utiliser ce type de structure pour étudier la mobilité des charges au sein d'une couche diélectrique. / One of the intrinsic properties of dielectrics is to accumulate electrical charges when subjected to external stresses (temperature, electrical field ...). This property can be helpful for some applications (DRAM...), but leads generally to failure of the device (micro-system...). Thus, a charge density measurement technics is mandatory for the scale of relevance according to the observed system. However due to miniaturization, the measurement technics classically used are helpless to study tiny systems of a few tens nanometers thick, as their spatial resolution is of the order a few micrometers. A new measurement technics represented by KPFM (Kelvin Probe Microscopy) and based on near field microscopy technology, can measure charges on a material with nanoscale lateral resolution. Our purpose here is to characterize charges injection and decay mechanisms in thin SiOxNy and SiNx film deposited by plasma process, thanks to near field microscopy. To achieve this goal, two approaches have been explored. The first one consists in localized injection of electrical charges at the surface of a thin SiOxNy layer of variable thickness (between 6 nm and 130nm) and to measure surface potential modification induced by injected charges. Surface potential (KPFM) and current (C-AFM) measurements coupled to electric field simulation by finite element (COMSOL(r)) emphasizes that two mechanisms are involved during charges injection: trapping and conduction through the layer. For thinner layers, conduction mechanism is predominant (which limits trapped charges amount); while for thicker films trapping is the main mechanism. For intermediate thickness films both mechanisms are in competition. Once the charges injected, dissipation in volume appears to be the predominant mechanism for any thickness. The second approach is the study of charges injection and transport between two embedded lateral electrodes. This structure allows overcoming the lack of in-depth sensitivity of the KPFM measurement toward the position of charges in the volume, to study injection phenomena at interfaces and transport of charges within the volume under electrical field constraint. The electric field induced between the two polarized electrodes was simulated by finite element using COMSOL and compared to surface potential measured by KFM. Results emphasize technical issues related to charges injection/transport between lateral electrodes. According to this analysis an experimental set up and data post-treatment protocol is developed which permits to characterized charges injection at interface. Besides, feasibility of charges mobility investigation using this type of structure was demonstrated.

Magister Scientiae - MSc (Chemistry) / Blending polymers together offers researchers the ability to create novel materials that have a combination of desired properties of the individual polymers for a variety of functions as well as improving specific properties. The behaviour of the resulting blended polymer or blend is determined by the interactions between the two polymers. The resultant synergy from blending an intrinsically conducting polymer like polyaniline (PANI), is that it possesses the electrical, electronic, magnetic and optical properties of a metal while retaining the poor mechanical properties, solubility and processibility commonly associated with a conventional polymer. Aromatic polyamic acid has outstanding thermal, mechanical, electrical, and solvent resistance properties that can overcome the poor mechanical properties and instability of the conventional conducting polymers, such as polyaniline.

Submitted by DIEGO ROSSI null (rossi_diego@ig.com.br) on 2016-02-16T18:58:22Z No. of bitstreams: 1 Dissertação D.Rossi - FINAL.pdf: 4611767 bytes, checksum: 71f830e143f447c9e962c2305462a623 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-02-17T16:11:21Z (GMT) No. of bitstreams: 1 rossi_d_me_bauru.pdf: 4611767 bytes, checksum: 71f830e143f447c9e962c2305462a623 (MD5) / Made available in DSpace on 2016-02-17T16:11:21Z (GMT). No. of bitstreams: 1 rossi_d_me_bauru.pdf: 4611767 bytes, checksum: 71f830e143f447c9e962c2305462a623 (MD5) Previous issue date: 2015-12-21 / Este trabalho tem por finalidade a deposição de filmes finos de carbono amorfo hidrogenado (a-C:H) e de filmes finos de carbono amorfo hidrogenado com silício (a-C:H:Si). Analisar a incorporação gradativa de cloro nos filmes, tornando-os clorados (a-C:H:Cl e a-C:H:Si:Cl). As técnicas utilizadas para a deposição dos filmes foram: (i) a deposição à vapor químico assistido por plasma (PECVD) e (ii) implantação iônica por imersão em plasma (PIIID). Os filmes foram produzidos a partir de misturas de vapores de propanol, CH3(CH2)2OH, vapores de tetrametilsilano, Si(CH3)4, vapores de clorofórmio, CHCl3, e argônio, Ar, respectivamente monômero 1, monômero 2, comonômero e gás plasmogênico. O aumento do clorofórmio na alimentação do reator acarretou em mudanças nas estruturas químicas do material depositado e também alterações nas suas características ópticas. Para averiguar as modificações nas propriedades ópticas dos filmes foram calculados o coeficiente de absorção, o índice de refração e o gap óptico com base em espectros de transmitância óptica na região do Ultravioleta, Visível e Infravermelho Próximo, (Uv/Vis/NIR). As modificações nas estruturas químicas dos filmes foram analisadas por espectroscopia de absorção no infravermelho por transformada de Fourier, FTIR, visando revelar os grupos químicos presentes nos filmes. Espectroscopia de fotoelétrons de raios X, (XPS), foi a técnica utilizada para desvendar a composição química elementar dos filmes e a 6concentração dos elementos presentes. As características de molhabilidade dos filmes foram medidas em um goniômetro, através da análise da interação da gota de um fluído com a superfície dos filmes. Espessuras medidas por perfilômetria foram comparadas a valores teóricos provenientes das constantes ópticas. Os resultados do XPS demonstraram a presença de cloro nos filmes, a concentração máxima obtida foi de ~ 8% at. Houve um aumento na taxa de deposição dos filmes em função do aumento da proporção de clorofórmio na entrada do reator. O ângulo de contato apresentou-se em torno de 75° para os filmes aC:H:Cl e em torno de 80° para os filmes a-C:H:Si:Cl. As análises ópticas Uv/Vis/NIR apresentaram índice de refração de ~1.5, calculadas por modelos computacionais iterativos, o gap de Tauc aumentou de 1,9 eV para 2,5 eV para filmes finos a-C:H clorados. / Thin hydrogenated amorphous carbon (a-C:H) and (a-C:H:Si) films were produced and the gradual incorporation of chlorine turn into a-C:H:Cl films and aC:H:Si:Cl films. The a-C:H:Cl and a-C:H:Si:Cl films were produced by plasma enhanced chemical vapor deposition (PECVD) from mixtures of vapor of propane, CH3(CH2)2OH, tetramethylsilane, Si(CH3)4, chloroform, CHCl3, and argon gas, Ar; respectively monomer 1, monomer 2, comonomer and argon gas. The increase of chloroform in the film composition resulted in changes in the chemical structure of the material and also changes in its optical characteristics. To investigate the changes in the optical properties of the films, the absorption coefficient, refractive index and band gap were calculated from optical transmittance spectra in the Ultraviolet, Visible and Near Infrared (Uv/Vis/NIR) regions. The modifications in chemical structures of the films were analyzed by Fourier transform infrared spectroscopy FTIR. X-ray photoelectron spectroscopy (XPS) was the technique used to measure the chemical composition of the films. The wettability characteristics were measured using a goniometer, through the analysis of the interaction of a fluid drop on the surface of the films. Film thicknesses were measured using perfilometry and compared with theoretical values derived from optical data. The XPS results showed chlorine in the film, and the maximum concentration was about 8% at. There was an increase in the deposition rate as 8chloroform proportion reactor inlet was added. The contact angle showed around 75° to a-C:H:Cl films and around 80° to a-C:H:Si:Cl films. The optical analyses Uv/Vis/NIR showed refractive index of ~1.5, calculated for interactive computer models. The Tauc band gap increased from 1,9 eV to 2,5 eV for a-C:H chlorinated films.

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-04-24Bitstream added on 2014-06-13T19:21:30Z : No. of bitstreams: 1 souza_ecf_dr_araiq.pdf: 1912726 bytes, checksum: 2307761479da3506d743212298df0f82 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nesta tese estudou-se a preparação de filmes finos de PZT não dopados e dopados com Nióbio, depositados sobre substratos de Pt/Ti/SiO2/Si para aplicações em memórias não voláteis de acesso randômico (NVRAM) e memórias ferroelétricas de acesso randômico (FeRAM). A dopagem dos filmes de PZT com Nióbio foi realizada visando obter valores ótimos nas propriedades ferroelétricas para a aplicação destes filmes como memórias ferroelétricas. Todavia, problemas como imprint, corrente de fuga e fadiga na polarização, estão presentes nos dispositivos de memórias contendo filmes de PZT sobre substratos platinizados. Para tentar resolver estes problemas, estudamos a produção de eletrodos de LaNiO3 depositados sobre substratos de SiO2/Si, para substituição dos substratos com eletrodos de Pt na preparação de filmes de PZT. Além disso, a dopagem do PZT com Nb levou a uma melhoria na resistência à fadiga em substratos platinizados. Os filmes foram preparados pelo método das soluções precursoras poliméricas. A influência do tratamento térmico, em forno convencional e em forno microondas, nas propriedades microestruturais e ferroelétricas dos filmes também foi avaliada. / In this thesis, we have studied the preparation of non-doped and Nb-doped PZT thin films deposited on Pt/Ti/SiO2/Si substrates for applications in NVRAM and FeRAM devices. Nb doping of PZT films produces good values of ferroelectric properties for the application as ferroelectric memories. PZT films on Pt electrodes present imprint, fatigue and leakage current. We have prepared LaNiO3 films on SiO2/Si substrates to substitute Pt electrodes. Moreover, Nb-doped PZT films deposited on Pt electrodes lead to improved fatigue resistance when compared with non doped PZT films. Non-doped and Nb-doped PZT thin films and LaNiO3 thin films were deposited by the polymeric precursor method. The influence of the thermal treatment in conventional and microwaves oven on the microstructural and ferroelectric properties was evaluated.

Metal thin films deposited on weakly-interacting substrates constitute an essential element of numerous microelectronic, catalytic, and optical devices. However, the natural tendency of metal atoms to agglomerate, upon condensation on a weakly-interacting surface, in dispersed three-dimensional (3D) islands affects negatively the performance of the above-mentioned devices. The aim of this thesis is to investigate one of the mechanisms governing silver (Ag) 3D island growth on weakly-interacting substrates, i.e. the nucleation of a new layer on the island top. Kinetic Monte Carlo (KMC) simulations are employed to calculate the top island-layer critical radius Rc required for nucleating a new layer in the out-of-plane direction. Single-island simulations are performed for growth temperatures T in the range 250 to 500 K and ratios of the pairwise adatom/substrate atom bond strength EB,sub to the corresponding adatom/adatom value EB,film in the range 0.5 to 0.75. We find that for T values below 250 K the islands exhibit a 2D morphology for all EB,sub/EB,film ratios. In contrast, for T values above 300 K there exists a range of relatively small EB,sub/EB,film values, where 2D morphology dominates. To calculate Rc for each island layer as the island shape evolves, a subroutine is developed and implemented in an existing KMC algorithm. Rc values are computed for 3D island growth at EB,sub/EB,film = 0.5 in the T range 300−500 K and the results show that Rc decreases monotonously from 17.3 to 6.0 Å and saturates approximately at 375 K. This trend is opposite to the typical behavior of islands grown under homoepitaxial conditions, for which the enhancement of downward inter-layer diffusion caused by an increase of T leads to lower atomic densities on the top, i.e. to a lower nucleation probability, and thus to an increase of Rc. This work contributes to the understanding of the physical processes that control thin-film morphological evolution; which is paramount for controlling and manipulating film growth for specific applications.

Master of Science / Electrical and Computer Engineering / William B. Kuhn / At RF frequencies and beyond, metallic circuit interconnects no longer behave as lumped-element wires; instead they exhibit distributed-element behavior and are classified as transmission lines. Power losses on transmission lines are of great concern to RF and microwave engineers and great care is taken to minimize power losses while still maintaining application-based robustness. The combination of low-temperature co-fire ceramics (LTCCs) and thin-film transmission line fabrication allows application-specific robustness and excellent microwave and millimeter wave performance to be achieved. LTCC technology provides a low-loss microwave substrate and allows for thin-film metal and insulator depositions to form precision transmission-line geometries and surface-applique capacitors. In the field of thin-film metals however, concern over excess power losses at high frequencies has arisen due to the necessity of a high-resistance metallic adhesion layer which is required for the mechanical adhesion of the transmission lines to the LTCC substrate. This is especially worrisome in a microstrip configuration where the current density is concentrated at the substrate-metal interface; exactly where the high-loss metal is situated. This thesis shows that if the high-resistance adhesion layer is limited to a thickness which is a fraction of its skin depth, with more conductive metals layered above, then those excessive resistive losses can be avoided. Issues with decreasing the total thickness of the thin-film layered metals are also investigated to achieve better interconnect line-and-space resolution, which is required for electronics operating at millimeter-wave bandwidths. Several test cases show that thinning of the metal layers has minimal impact on electrical performance. However, poor signal integrity is observed when the finished thickness of the metal stack up is reduced below 1μm. Further testing reveals that surface roughness leads to manufacturing issues when trying to produce thin-films with thicknesses in the sub-micron range. Finally, a novel bypass and coupling capacitor topology is proposed and investigated. The capacitors are simple thin-film metal-insulator-metal constructions designed for use in a flip-chip mounting environment. Testing shows the capacitors exhibit a very low impedance through 20 GHz making them an ideal board-level bypass solution. This technology has the potential to replace all but the large bulk charge storage capacitors in electronic designs, increasing performance and mechanical robustness, while simultaneously decreasing bill of material cost and PCB assembly times.

abstract: GaAs single-junction solar cells have been studied extensively in recent years, and have reached over 28 % efficiency. Further improvement requires an optically thick but physically thin absorber to provide both large short-circuit current and high open-circuit voltage. By detailed simulation, it is concluded that ultra-thin GaAs cells with hundreds of nanometers thickness and reflective back scattering can potentially offer efficiencies greater than 30 %. The 300 nm GaAs solar cell with AlInP/Au reflective back scattering is carefully designed and demonstrates an efficiency of 19.1 %. The device performance is analyzed using the semi-analytical model with Phong distribution implemented to account for non-Lambertian scattering. A Phong exponent m of ~12, a non-radiative lifetime of 130 ns, and a specific series resistivity of 1.2 Ω·cm2 are determined. Thin-film CdTe solar cells have also attracted lots of attention due to the continuous improvements in their device performance. To address the issue of the lower efficiency record compared to detailed-balance limit, the single-crystalline Cd(Zn)Te/MgCdTe double heterostructures (DH) grown on InSb (100) substrates by molecular beam epitaxy (MBE) are carefully studied. The Cd0.9946Zn0.0054Te alloy lattice-matched to InSb has been demonstrated with a carrier lifetime of 0.34 µs observed in a 3 µm thick Cd0.9946Zn0.0054Te/MgCdTe DH sample. The substantial improvement of lifetime is due to the reduction in misfit dislocation density. The recombination lifetime and interface recombination velocity (IRV) of CdTe/MgxCd1-xTe DHs are investigated. The IRV is found to be dependent on both the MgCdTe barrier height and width due to the thermionic emission and tunneling processes. A record-long carrier lifetime of 2.7 µs and a record-low IRV of close to zero have been confirmed experimentally. The MgCdTe/Si tandem solar cell is proposed to address the issue of high manufacturing costs and poor performance of thin-film solar cells. The MBE grown MgxCd1-xTe/MgyCd1-yTe DHs have demonstrated the required bandgap energy of 1.7 eV, a carrier lifetime of 11 ns, and an effective IRV of (1.869 ± 0.007) × 103 cm/s. The large IRV is attributed to thermionic-emission induced interface recombination. These understandings can be applied to fabricating the high-efficiency low-cost MgCdTe/Si tandem solar cell. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015

abstract: Mechanical behavior of metallic thin films at room temperature (RT) is relatively well characterized. However, measuring the high temperature mechanical properties of thin films poses several challenges. These include ensuring uniformity in sample temperature and minimizing temporal fluctuations due to ambient heat loss, in addition to difficulties involved in mechanical testing of microscale samples. To address these issues, we designed and analyzed a MEMS-based high temperature tensile testing stage made from single crystal silicon. The freestanding thin film specimens were co-fabricated with the stage to ensure uniaxial loading. Multi-physics simulations of Joule heating, incorporating both radiation and convection heat transfer, were carried out using COMSOL to map the temperature distribution across the stage and the specimen. The simulations were validated using temperature measurements from a thermoreflectance microscope. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2016

abstract: The work contained in this dissertation is focused on the structural and optical properties of III-V semiconductor structures for solar cell applications. By using transmission electron microscopy, many of their structural properties have been investigated, including morphology, defects, and strain relaxation. The optical properties of the semiconductor structures have been studied by photoluminescence and cathodoluminescence. Part of this work is focused on InAs quantum dots (QDs) embedded in AlGaAs matrices. This QD system is important for the realization of intermediate-band solar cells, which has three light absorption paths for high efficiency photovoltaics. The suppression of plastic strain relaxation in the QDs shows a significant improvement of the optoelectronic properties. A partial capping followed by a thermal annealing step is used to achieve spool-shaped QDs with a uniform height following the thickness of the capping layer. This step keeps the height of the QDs below a critical value that is required for plastic relaxation. The spool-shaped QDs exhibit two photoluminescence peaks that are attributed to ground and excited state transitions. The luminescence peak width is associated with the QD diameter distribution. An InAs cover layer formed during annealing is found responsible for the loss of the confinement of the excited states in smaller QDs. The second part of this work is focused on the investigation of the InxGa1-xN thin films having different bandgaps for double-junction solar cells. InxGa1-xN films with x ≤ 0.15 were grown by metal organic chemical vapor deposition. The defects in films with different indium contents have been studied. Their effect on the optical properties of the film have been investigated by cathodoluminescence. InxGa1-xN films with indium contents higher than 20% were grown by molecular beam epitaxy. The strain relaxation in the films has been measured from electron diffraction patterns taken in cross-sectional TEM specimens. Moiré fringes in some of the films reveal interfacial strain relaxation that is explained by a critical thickness model. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016