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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
311

Epitaxial growth and optical properties of Mg3N2, Zn3N2, and alloys

Wu, Peng 24 April 2019 (has links)
Zinc nitride and magnesium nitride are examples of the relatively unexplored II3V2 group of semiconductor materials. These materials have potential applications in the electronics industry due to their excellent optical and electrical properties. This study mainly focuses on the growth and characterization of the new semiconductor materials: zinc nitride, magnesium nitride, and their alloys. The (100) oriented zinc nitride thin films were grown on both (110) sapphire substrates and (100) MgO substrates by plasma-assisted molecular beam epitaxy (MBE). The typical growth rate is in the range of 0.02-0.06 nm/s, the growth temperature is in the range of 140-180 oC, and background nitrogen pressure is around 10-5 Torr. The growth process was monitored by in-situ: reflection high energy electron diffraction (RHEED) and optical reflectivity. The RHEED and X-ray diffraction patterns of the zinc nitride indicate that the film is a single crystal material. The in-situ optical reflectivity pattern of the zinc nitride shows interference oscillations, and these oscillations are damped out as the thickness increases. The reflectivity as a function of time was accurately simulated by an optical equation. The optical constants of the thin films, the growth rate, and the thickness were derived from the simulation of the in-situ reflectance. The X-ray diffraction shows that (400) oriented zinc nitride thin films were grown on both A-plane (110) sapphire substrates and (100) MgO substrates. Optical transmittance measurements were performed on the zinc nitride thin films. The spectrum of the zinc nitride transmittance indicates that zinc nitride has a high optical absorption in the visible light region. The absorption coefficient was calculated from the transmittance spectrum, and the optical band gap of the zinc nitride thin film was found to be 1.25-1.28 eV. Ellipsometry measurements suggested that the refractive index of zinc nitride is 2.3-2.7, and the extinction coefficient is ~0.5-0.7 in the energy range 1.5-3.0 eV. The electron transport measurement shows that the single crystal zinc nitride has a mobility as high as 395 cm2 /Vs. A plasma-assisted MBE system was employed for magnesium nitride growth. The growth temperature was in the range of 300-350 oC. RHEED and laser reflectivity were employed during growth. The RHEED and X-ray diffraction patterns indicated that the epilayers are single crystal films. The optical laser reflectivity was well fitted by a modified optical equation. The optical constants and growth rate were derived from the simulation. X-ray diffraction showed that (400) oriented single crystal magnesium nitride films were grown on (100) MgO substrates. The optical transmittance spectra show that the magnesium nitride has a high absorption below 500 nm. The calculated absorption coefficient is as high as 4x10-4 cm-1 in the range of ~2.5-3.0 eV. The optical band gap was estimated to be ~2.5 eV. Ellipsometry measurements showed that the refractive index of the magnesium nitride is 2.3-2.75 and the extinction coefficient is less than 0.3 in the energy range of 1.5-3.0 eV. Zinc nitride-magnesium nitride (Zn3-3xMg3xN2) alloys were grown on (100) YSZ substrates by sputtering. The bandgap ranged from 1.2 eV to 2.1 eV for Mg content x in the 0-0.59 range. One film with a bandgap of ~1.4 eV and Mg content of 0.18 has the relatively high mobility of 47 cm2 /Vs which was expected for photovoltaics application. / Graduate
312

Vers un laser germanium dopé N et contraint en tension / Towards a tensile strained, N doped germanium laser

Kersauson, Malo de 26 June 2013 (has links)
Dans ce travail de thèse, nous avons étudié différentes approches qui devraient permettre d’obtenir l’effet laser dans le germanium. Nous avons pu montrer expérimentalement l’influence du dopage et de la déformation sur la structure de bande du germanium, et l’adéquation avec les modèles concluants à l’existence de gain. Nous avons exploré les possibilités offertes par l’hétéro-épitaxie sur III-V pour obtenir une déformation en tension du germanium. Nous avons évalué la déformation résultante par des mesures croisées de rayons X, de diffusion Raman et de photoluminescence, et étudié l’évolution de la qualité des couches épitaxiées en fonction de la déformation et de l’épaisseur. Une nouvelle méthode de déformation du germanium, s’appuyant sur le dépôt par plasma de couches contraintes de nitrure, a été introduite et étudiée. L’effet laser a été recherché par la conception de guides ridges et microdisques déformés par ces dépôts. Plusieurs voies d’application de la déformation dans ces cavités ont été explorées à travers des simulations par éléments finis et la conception de structures de test. Cette optimisation préalable nous a permis d’observer sur les microdisques une déformation biaxiale de 1.11%. En uniaxial, nous avons pu appliquer au germanium une déformation de 1.07% et montrer expérimentalement l’importance de la direction de la déformation dans l’augmentation de la luminescence. Nous avons pu observer et mesurer un gain optique net de 80 cm⁻¹ dans des structures déformées uniaxialement à 0.8%. / In this PhD work, we studied different approaches that should lead to a germanium laser. We have experimentally shown the influence of strain and doping on the germanium band structure, and the adequacy of the existing models. We explored the possibilities offered by heteroepitaxy on III-V compounds to apply stress. We investigated the resulting strain by cross-checking X-rays, Raman spectroscopy and photoluminescence measurements, and analysed the quality of the grown layers depending on strain and thickness. A new method to apply strain to the germanium, by means of plasma deposited stressed nitride layers, was introduced and studied. Lasing has been pursued by conceiving ridges and microdisks strained by this method. An optimization of the geometry was performed through finite element modeling and the production of test structures. This optimization allowed to achieve a maximum biaxial strain of 1.1%. For uniaxial strains, we observed a maximum of 1.07% and showed experimentally the importance of the crystalline orientation in the enhancement of the emission. We demonstrated a modal gain value of 80 cm⁻¹ in ridges uniaxially strained at 0.8%.
313

Photoluminescent properties of GaAs₁₋xNx epitaxial layers on GaAs substrates =: 砷鎵化上砷氮化鎵外延層的光致發光性質. / 砷鎵化上砷氮化鎵外延層的光致發光性質 / Photoluminescent properties of GaAs₁₋xNx epitaxial layers on GaAs substrates =: Shen jia hua shang shen dan hua jia wai yan ceng de guang zhi fa guang xing zhi. / Shen jia hua shang shen dan hua jia wai yan ceng de guang zhi fa guang xing zhi

January 2001 (has links)
by Lam Siu Dan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 65-67). / Text in English; abstracts in English and Chinese. / by Lam Siu Dan. / Table of contents --- p.I / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Interest in GaAs1-xNx/GaAs alloy --- p.1 / Chapter 1.2 --- Interest in growing GaAs1-xNx/GaAs using different carrier gases --- p.4 / Chapter 1.3 --- Theoretical calculation of the band gap energy of GaAs1-xNx alloy --- p.4 / Chapter 1.4 --- Advantages of using photoluminescence (PL) --- p.7 / Chapter 1.5 --- Our work --- p.9 / Chapter Chapter 2 --- Experimental setup and procedures / Chapter 2.1 --- Growth conditions of GaAs1-xNx on (001) GaAs --- p.10 / Chapter 2.2 --- X-ray diffraction / Chapter 2.2.1 --- Setup --- p.12 / Chapter 2.2.2 --- Types of X-ray measurements --- p.12 / Chapter 2.3 --- PL measurements / Chapter 2.3.1 --- Setup --- p.14 / Chapter 2.3.2 --- Types of PL measurement --- p.16 / Chapter Chapter 3 --- Results and discussions / Chapter 3.1 --- X-ray diffraction of GaAs1-xNx/GaAs / Chapter 3.1.1 --- GaAs1-xNx/GaAs grown using H2 as carrier gas --- p.17 / Chapter 3.1.2 --- GaAs1-xNx/GaAs grown using N2 as carrier gas --- p.28 / Chapter 3.1.3 --- Peak widths of the X-ray rocking curves of GaAs1-xNx/GaAs --- p.30 / Chapter 3.2 --- Room temperature (RT) and 10K PL of GaAs1-xNx/GaAs / Chapter 3.2.1 --- The energy of the NBE peak of GaAs1-xNx/GaAs --- p.32 / Chapter 3.2.2 --- The width of the NBE peak of GaAs1-xNx/GaAs --- p.44 / Chapter 3.3 --- Excitation power density (EPD) dependent PL studies of GaAs1-xNx/GaAs / Chapter 3.3.1 --- The energy of the NBE peak of GaAs1-xNx/GaAs --- p.49 / Chapter 3.3.2 --- The width of the NBE peak of GaAs1-xNx/GaAs --- p.55 / Chapter 3.4 --- Temperature dependent PL studies of GaAs1-xNx/GaAs --- p.57 / Chapter Chapter 4 --- Conclusions --- p.62 / References --- p.63
314

The electrical and optical characterization of the InGaAs/InP alloy system

Towe, Elias D January 1981 (has links)
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Elias D. Towe. / M.S.
315

Monolithic Heterovalent Integration of Compound Semiconductors and Their Applications

January 2019 (has links)
abstract: Compound semiconductors tend to be more ionic if the cations and anions are further apart in atomic columns, such as II-VI compared to III-V compounds, due in part to the greater electronegativity difference between group-II and group-VI atoms. As the electronegativity between the atoms increases, the materials tend to have more insulator-like properties, including higher energy band gaps and lower indices of refraction. This enables significant differences in the optical and electronic properties between III-V, II-VI, and IV-VI semiconductors. Many of these binary compounds have similar lattice constants and therefore can be grown epitaxially on top of each other to create monolithic heterovalent and heterocrystalline heterostructures with optical and electronic properties unachievable in conventional isovalent heterostructures. Due to the difference in vapor pressures and ideal growth temperatures between the different materials, precise growth methods are required to optimize the structural and optical properties of the heterovalent heterostructures. The high growth temperatures of the III-V materials can damage the II-VI barrier layers, and therefore a compromise must be found for the growth of high-quality III-V and II-VI layers in the same heterostructure. In addition, precise control of the interface termination has been shown to play a significant role in the crystal quality of the different layers in the structure. For non-polar orientations, elemental fluxes of group-II and group-V atoms consistently help to lower the stacking fault and dislocation density in the II-VI/III-V heterovalent heterostructures. This dissertation examines the epitaxial growth of heterovalent and heterocrystalline heterostructures lattice-matched to GaAs, GaSb, and InSb substrates in a single-chamber growth system. The optimal growth conditions to achieve alternating layers of III-V, II-VI, and IV-VI semiconductors have been investigated using temperature ramps, migration-enhanced epitaxy, and elemental fluxes at the interface. GaSb/ZnTe distributed Bragg reflectors grown in this study significantly outperform similar isovalent GaSb-based reflectors and show great promise for mid-infrared applications. Also, carrier confinement in GaAs/ZnSe quantum wells was achieved with a low-temperature growth technique for GaAs on ZnSe. Additionally, nearly lattice-matched heterocrystalline PbTe/CdTe/InSb heterostructures with strong infrared photoluminescence were demonstrated, along with virtual (211) CdZnTe/InSb substrates with extremely low defect densities for long-wavelength optoelectronic applications. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019
316

Next generation mid-wave infrared cascaded light emitting diodes: growth of broadband, multispectral, and single color devices on GaAs and integrated circuits

Provence, Sydney R. 01 August 2016 (has links)
InAs/GaSb superlattices are an attractive material system for infrared light emitting diodes, due to the ability to tune the band gap throughout most of the infrared regime. A key consideration in the epitaxial growth of these heterostructures is crystalline material quality. In developing thick layers of epitaxially grown material, there are moderate amounts of elastic strain that can be incorporated into a heterostructure, beyond which deformations will form that will alleviate the lattice mismatch. This thesis investigates the optical and electronic properties of lattice-mismatched and strained materials through the study of thick dual-color light emitting diodes, broadband light emitting diodes, and InAs/GaSb superlattice devices developed on GaAs substrates and GaAs integrated circuits. A dual-color infrared light emitting diode is demonstrated emitting in the mid-wave infrared band at 3.81 μm and 4.72 μm. The design of the device stacks two independently operable InAs/GaSb superlattices structures on top of one another, so that 10 μm of material is grown with molecular beam epitaxy. Each layer is lattice-matched to a GaSb substrate. At quasi-continuous operation, radiances of 5.48 W/cm2-sr and 2.67 W/cm2-sr are obtained. A broadband light emitting diode spanning the mid-wave infrared is demonstrated with eight stages of InAs/GaSb superlattices individually tuned to a different color. The performance of the device is compared with an identical eight stage device emitting in the middle of the mid-wave infrared. The emission of the fabricated broadband device spans from 3.2 μm to 6 μm with peak radiance of 137.1 mW/cm2-sr. Growth of antimonide-based devices on GaAs is desirable to the relative transparency of semi-insulating substrates throughout the infrared, and as semi-insulating GaSb substrates are not available. The growth of bulk GaSb on GaAs is explored through different techniques in order to confine relaxation due to lattice mismatch strain to the GaSb/GaAs interface. A low temperature nucleation technique with a thin GaSb wetting layer is found to have the best overall surface morphology, although screw dislocations are a prominent feature on all samples. The dislocations and overall surface roughness are not found to destructively impact the overall device quality, as four stage InAs/GaSb superlattice devices grown on GaAs substrates are found to have superior electroluminescent emission and external quantum efficiency compared to an identical device grown on a GaSb substrate due to the higher substrate transparency and superior thermal properties. Epitaxy on electronics growth techniques on GaAs integrated circuits are developed to bypass the hybridization process in light emitting diode development. Chips obtained from Quorvo, Inc. are found to endure ultra-high vacuum molecular beam epitaxy environment at higher temperatures with silicon nitride encapsulation, and a low temperature oxide removal technique is developed using an atomic hydrogen source. Chemical-mechanical polishing techniques are developed to create an “epi-ready” substrate surface. Ultimately, no photoluminescent emission is observed from InAs/GaSb superlattices grown on GaAs integrated circuits, although electroluminescent emission is still possible.
317

CVD Growth of SiC on Novel Si Substrates

Myers, Rachael L 27 October 2003 (has links)
Silicon Carbide has been a semiconductor material of interest as a high power and temperature replacement for Silicon (Si) in harsh environments due to the higher thermal conductivity and chemical stability of SiC. The cost, however, to produce this material is quite high. There are also defects in the substrate material (SiC) that penetrate into the active devices layers which are known device killers. Silicon is a material that provides a low cost substrate material for epitaxial growth and does not contain the defects that SiC substrates have. However, the large (~22%) lattice mismatch between Si and SiC creates dislocations at the SiC/Si interface and defects in the SiC epitaxial layer. These defects result in high leakage currents in 3C-SiC/Si devices. The main focus of the this research was to reduce or eliminate these defects using novel Si substrates. First a 3C-SiC on Si baseline process was developed under atmospheric pressure conditions consisting of 3 steps - an in-situ hydrogen etch to remove the native oxide, a carbonization step to convert the Si surface to SiC, and finally a growth step to thicken the SiC layer to the desired value. This process was then modified to establish a high-quality, low-pressure 3C-SiC CVD growth process. This LPCVD process was then used to grow 3C-SiC on numerous novel Si substrates, including porous Si, porous 3C-SiC "free-standing" substrates and SOI substrates which consisted on thin Si films bonded to poly-crystalline SiC plates. The results of these experiments are presented along with suggestions for future work so that device-grade films of 3C-SiC can be developed for various applications.
318

Characterisation of Group III nitrides using hard X-ray synchrotron radiation

Mudie, Stephen January 2004 (has links)
Abstract not available
319

Silicon surface passivation and epitaxial growth on c-Si by low temperature plasma processes for high efficiency solar cells

Labrune, Martin 20 May 2011 (has links) (PDF)
This thesis presents a work which has been devoted to the growth of silicon thin films on crystalline silicon for photovoltaic applications by means of RF PECVD. The primary goal of this work was to obtain an amorphous growth on any c-Si surface in order to provide an efficient passivation, as required in heterojunction solar cells. Indeed, we demonstrated that epitaxial or mixed phase growths, easy to obtain on (100) Si, would lead to poor surface passivation. We proved that growing a few nm thin a-Si1-xCx:H alloy film was an efficient, stable and reproducible way to hinder epitaxy while keeping an excellent surface passivation by the subsequent deposition of a-Si:H films. Process optimization mainly based on Spectroscopic Ellipsometry, Effective lifetime measurements (Sinton lifetime tester) and current-voltage characterization led us to demonstrate that it was possible to obtain a-Si:H/c-Si heterojunction solar cells with stable VOC of 710 mV and FF of 76 % on flat (n) c-Si wafers, with solar cells of 25 cm2 whose metallization was realized by screen-printing technology. This work has also demonstrated the viability of a completely dry process where the native oxide is removed by SiF4 plasma etching instead of the wet HF removal. Last but not least, the epitaxial growth of silicon thin films, undoped and n or p-type doped, on (100)-oriented surfaces has been studied by Spectroscopic Ellipsometry and Hall effect measurements. We have been able to fabricate homojunction solar cells with a p-type emitter as well as p-i-n structures with an undoped epitaxial absorber on a heavily-doped (p) c-Si wafers.
320

Growth, structural, electronic and optical characterization of nitride semiconductors

Constantin, Costel. January 2005 (has links)
Thesis (Ph.D.)--Ohio University, November, 2005. / Title from PDF t.p. Includes bibliographical references (p. 89-93)

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