京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19720号 / 工博第4175号 / 新制||工||1644(附属図書館) / 32756 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 田中 勝久, 准教授 掛谷 一弘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19721号 / 工博第4176号 / 新制||工||1644(附属図書館) / 32757 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 藤田 静雄, 教授 髙岡 義寛, 准教授 須田 淳 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

While investigations of semiconductor nanowires (NWs) has a long history, a significant progress is yet to be made in silicon carbide (SiC) NW technologies before they are ready to be utilized in electronic applications. In this dissertation work, SiC NW polytype control, NW axis orientation with respect to the growth substrate and other issues of potential technological importance are investigated. A new method for growing SiC NWs by vapor-liquid-solid mechanism was developed. The method is based on an in-situ vapor phase delivery of a metal catalyst to the growth surface during chemical vapor deposition. This approach is an alternative to the existing seeded catalyst method based on ex-situ catalyst deposition on the target substrate. The new SiC NW growth method provided an improved control of the NW density. It was established that the NW density is influenced by the distance from the catalyst source to the substrate and is affected by both the gas flow rate and the catalyst diffusion in the gas phase. An important convenience of the new method is that it yields NW growth on the horizontal substrate surfaces as well as on titled and vertical sidewalls of 4H-SiC mesas. This feature facilitates investigation of the NW growth trends on SiC substrate surfaces having different crystallographic orientations simultaneously, which is very promising for future NW device applications. It was established that only certain orientations of the NW axes were allowed when growing on a SiC substrate. The allowed orientations of NWs of a particular polytype were determined by the crystallographic orientation of the substrate. This substrate-dependent (i.e., epitaxial) growth resulted in growth of 3C-SiC NWs in total six allowed crystallographic orientations with respect to the 4H-SiC substrate. This NW axis alignment offers an opportunity to achieve a limited number of NW axis directions depending on the surface orientation of the substrate. The ease of controlling the NW density enabled by the vapor-phase catalyst delivery approach developed in this work, combined with the newly obtained knowledge about how to grow unidirectional (wellaligned) NW arrays, offer new opportunities for developing novel SiC NW electronic and photonic devices.

[pt] A integração monolítica de um modulador com um guia de onda é de muito interesse para aplicação em comunicações ópticas pelo fato de que podemos diminuir as perdas por acoplamento óptico entre os dois dispositivos e usar moduladores curtos que operem em altas taxas de transmissão de dados. O crescimento epitaxial seletivo é uma das técnicas mais promissoras na atualidade para aplicação na integração monolítica de dispositivos semicondutores. Esta técnica permite controlar a espessura e a tensão das camadas crescidas seletivamente permitindo otimizar a integração e as características das estruturas dos dispositivos. A tese trata da implementação, do estudo e da aplicação do crescimento epitaxial seletivo por MOCVD de estruturas casadas e tensionadas de poços quânticos múltiplos de InGaAs/InAlAs para a fabricação de moduladores de amplitude baseados no efeito Stark e sua integração com guias de onda. O desempenho dos moduladores, baseados em estruturas de poços quânticos múltiplos de InGaAs/InAlAs que operam em 1,55 ym, é notavelmente melhorado quando é introduzida uma composição de 52% de Ga na liga e se tem um poço de ~100 A de espessura. Nesse caso, os moduladores possuem uma elevada figura de mérito e podem ser insensíveis à polarização. Nesse estudo foram crescidas várias amostras onde foi analisado o aumento na taxa de crescimento e a variação na composição das ligas de InGaAs e InAlAs em material bulk e em poços quânticos de InGaAs/InAlAs em função da geometria da máscara utilizada, i.e. diferentes larguras do dielétrico e largura da janela onde ocorre o crescimento fixo. Finalmente foram processados guias de onda cujas estruturas foram crescidas com a técnica de crescimento seletivo. Esses guias foram caracterizados por técnicas de campo próximo. / [en] The monolithic integration of a modulator with a waveguide is a lot of interest for application in optical communications for the fact in that can decrease the losses for optical joining between the two devices and to use short modulators that operate in high rates of transmission data. The selective growth is at the present time, one the more promising technique for application in the monolithic integration of semiconductors device. This technique allows to control the thickness and the stress of the grown layers allowing to improve the integration and the characteristics of the devices structures. These thesis is about the implementation, study and application of the selectuve growth by MOCVD of both match and tensile structures of multi quantum wells of inGaAs/InAlAs for the production of the amplitude modulators based on the Stark effect and its integration with waveguide. The performance of the modulators based on structures of multi quantum wells of InGaAs/InAlAs operating in 1,55 um, is notably improved whena Ga composition of 52% is used and the thickness of a quantum well is near to ~100 A. In that case, the modulators have a high figured of merit and they can be insensitive to the polarization. In this study, several samples was grown and the growing rate increase was analyzed and the variation of the composition in InGaAs and InAlAs in bulk alloys and in quantum wells of InGaAs/InAlAs in function of the window where the growth is spent. Finally, waveguides were processed whose structures were grown with the technique of selective growth. Those guides were characterized by the near field technique.

GaN holds significant potential as a material for vertical p-n diodes, enabling the realization of devices with reverse breakdown voltages of 5 kV or higher. Carbon serves as the primary compensating dopant in the growth process, incorporated into GaN during metalorganic chemical vapor deposition (MOCVD) growth. The level of carbon incorporation depends on several factors, including growth rate, ammonia flow, temperature, pressure, and trimethylgallium (TMGa) flow. Through guided empirical modeling, it was demonstrated that the carbon incorporation in GaN growth could be predicted using a single parameter based on the ratio of ammonia flow to the growth rate. This model accurately predicts carbon concentrations ranging from 1x1017 to 5x1014 cm-3 while allowing for maximized growth rates. Other extrinsic dopants have either been reduced below the threshold of consideration or modeled using similar single-parameter relationships. By identifying the dominant extrinsic dopants and accounting for them, an intrinsic defect with a concentration of 2.2x1015 cm-3 was identified. By combining these relationships, growth conditions for n-GaN were optimized, resulting in electron concentrations as low as 1x1015 cm-3. Leveraging these techniques, p-n diodes were grown, achieving a reverse breakdown voltage as high as 3.1 kV. / Doctor of Philosophy / Power electronic devices based on vertical GaN have the potential to revolutionize applications such as electric vehicles, solar charging systems, and the smart grid. However, there are significant materials challenges that need to be addressed in order to realize these devices. They must be extremely pure and extremely thick. Unfortunately, the primary source of these materials also contains carbon, which can negatively impact purity. To overcome this challenge, an empirical model for the growth process has been developed. This model enables independent control over the carbon source and the removal of carbon, using a single parameter. By leveraging this model, it becomes possible to optimize the trade-off between high purity, high growth rates, and ideal electronic properties. Using these techniques, devices were grown with next-generation levels of performance at minimal time and cost.

No description available.

<p>Light emitting diode (LED)-based solid state displays (SSD) have attracted growing interest due to their advantages in terms of contrast ratio, brightness, viewing angle, and response time compared to liquid crystal displays. GaN based III-nitride thin film materials are suitable materials for SSD due to their wide and tunable bandgaps. However, the large size and costly manufacturing process of commercially available GaN-based LED chips limit the potential uses of LEDs as the pixels of SSD.</p> <p>In this work, tiny single crystal beta-phase (111) oriented SiC whiskers 2 microns in diameter and 18 microns in length are proposed as the substrates for GaN growth due to their small lattice constant mismatch (3%) with GaN, their conductive nature and their small size for potential use in SSD pixels. Aligned SiC whiskers with (111) planes exposed in an alumina matrix prepared by a precise manipulation and alignment method of SiC whiskers including a series of steps was developed in this work. The alignment degree of whiskers achieved in this work is higher than conventional extrusion methods, and a sintering approach capable of forming an aligned alumina/SiC composite was developed and understood using a self-limiting oxidation reaction mechanism.</p> <p>To take advantage of the potential versatility, scalability and cost effectiveness of sputtering for SSD manufacturing, a reactive sputtering system was built for a detailed investigation of GaN thin film growth nucleation and subsequent growth behavior on SiC. 6H-SiC single crystal substrates were chosen as a reference substrate for SiC whiskers. An XRRC indicates that a high quality single crystalline GaN thin film was successfully grown epitaxially on 6H-SiC by sputtering. Two-dimensional X-ray diffraction and scanning transmission electron microscopy results demonstrated that the epitaxial growth of GaN thin films relies on the short range order and/or crystalline area of the native oxide layer in GaN/SiC interface for the first time.</p> / Doctor of Philosophy (PhD)

Gallium nitride (GaN) and its related semiconductor alloys are attracting tremendous interest for their wide range of applications in blue and green LEDs, diode lasers, high-temperature and high-power electronics. Nanomaterials such as InGaN/GaN core-shell three-dimensional nanostructures are seen as a breakthrough technology for future solid-state lighting and nano-electronics devices. In a core-shell LED, the active semiconductor layers grown around a GaN core enable control over a wide range of wavelengths and applications. In this thesis the capability for the heteroepitaxial growth of a proof-of-principle core-shell LED is advanced. A design that can be applied at the wafer scale using metalorganic vapor phase epitaxy (MOVPE) crystal growth on highly uniform GaN nanorod (NR) structures is proposed. This project demonstrates understanding over the growth constraints of active layers and dopant layers. The impact of reactor pressure and temperature on the morphology and on the incorporated InN mole fraction was studied for thick InGaN shells on the different GaN crystal facets. Mg doping and effectiveness of the p-n junction for a core-shell structure was studied by extensive growth experiments and characterization. Sapphire and Si substrates were used, and at all the stages of growth and fabrication. The structures were optimized to achieve geometry homogeneity, high-aspect-ratio, incorporation homogeneity for InN and Mg dopant. The three-dimensional nature of NRs and their light emission provided ample challenges which required adaptation of characterization and fabrication techniques for a core-shell device. Finally, an electrically contacted core-shell LED is demonstrated and characterized. Achieving a proof-of-principle core-shell device could be the starting point in the development of nanostructure-based devices and new physics, or in solving technical problems in planar LEDs, such as the polarization of emitted light, the quantum-confined Stark effect, efficiency droop, or the green gap.

This dissertation describes the development of III-nitride (III-N) bipolar devices for optoelectronic and electronic applications. Research mainly involves device design, fabrication process development, and device characterization for Geiger-mode gallium nitride (GaN) deep-UV (DUV) p-i-n avalanche photodiodes (APDs), indium gallium nitride (InGaN)/GaN-based violet/blue laser diodes (LDs), and GaN/InGaN-based npn radio-frequency (RF) double-heterojunction bipolar transistors (DHBTs). All the epitaxial materials of these devices were grown in the Advanced Materials and Devices Group (AMDG) led by Prof. Russell D. Dupuis at the Georgia Institute of Technology using the metalorganic chemical vapor deposition (MOCVD) technique. Geiger-mode GaN p-i-n APDs have important applications in DUV and UV single-photon detections. In the fabrication of GaN p-i-n APDs, the major technical challenge is the sidewall leakage current. To address this issue, two surface leakage reduction schemes have been developed: a wet-etching surface treatment technique to recover the dry-etching-induced surface damage, and a ledged structure to form a surface depletion layer to partially passivate the sidewall. The first Geiger-mode DUV GaN p-i-n APD on a free-standing (FS) c-plane GaN substrate has been demonstrated. InGaN/GaN-based violet/blue/green LDs are the coherent light sources for high-density optical storage systems and the next-generation full-color LD display systems. The design of InGaN/GaN LDs has several challenges, such as the quantum-confined stark effect (QCSE), the efficiency droop issue, and the optical confinement design optimization. In this dissertation, a step-graded electron-blocking layer (EBL) is studied to address the efficiency droop issue. Enhanced internal quantum efficiency (ɳi) has been observed on 420-nm InGaN/GaN-based LDs. Moreover, an InGaN waveguide design is implemented, and the continuous-wave (CW)-mode operation on 460-nm InGaN/GaN-based LDs is achieved at room temperature (RT). III-N HBTs are promising devices for the next-generation RF and power electronics because of their advantages of high breakdown voltages, high power handling capability, and high-temperature and harsh-environment operation stability. One of the major technical challenges to fabricate high-performance RF III-N HBTs is to suppress the base surface recombination current on the extrinsic base region. The wet-etching surface treatment has also been employed to lower the surface recombination current. As a result, a record small-signal current gain (hfe) > 100 is achieved on GaN/InGaN-based npn DHBTs on sapphire substrates. A cut-off frequency (fT) > 5.3 GHz and a maximum oscillation frequency (fmax) > 1.3 GHz are also demonstrated for the first time. Furthermore, A FS c-plane GaN substrate with low epitaxial defect density and good thermal dissipation ability is used for reduced base bulk recombination current. The hfe > 115, collector current density (JC) > 141 kA/cm², and power density > 3.05 MW/cm² are achieved at RT, which are all the highest values reported ever on III-N HBTs.

abstract: This dissertation presents research findings regarding the exploitation of localized surface plasmon (LSP) of epitaxial Ag islands as a means to enhance the photoluminescence (PL) of Germanium (Ge) quantum dots (QDs). The first step of this project was to investigate the growth of Ag islands on Si(100). Two distinct families of Ag islands have been observed. “Big islands” are clearly faceted and have basal dimensions in the few hundred nm to μm range with a variety of basal shapes. “Small islands” are not clearly faceted and have basal diameters in the 10s of nm range. Big islands form via a nucleation and growth mechanism, and small islands form via precipitation of Ag contained in a planar layer between the big islands that is thicker than the Stranski-Krastanov layer existing at room-temperature. The pseudodielectric functions of epitaxial Ag islands on Si(100) substrates were investigated with spectroscopic ellipsometry. Comparing the experimental pseudodielectric functions obtained for Si with and without Ag islands clearly identifies a plasmon mode with its dipole moment perpendicular to the surface. This observation is confirmed using a simulation based on the thin island film (TIF) theory. Another mode parallel to the surface may be identified by comparing the experimental pseudodielectric functions with the simulated ones from TIF theory. Additional results suggest that the LSP energy of Ag islands can be tuned from the ultra-violet to the infrared range by an amorphous Si (α-Si) cap layer. Heterostructures were grown that incorporated Ge QDs, an epitaxial Si cap layer and Ag islands grown atop the Si cap layer. Optimum growth conditions for distinct Ge dot ensembles and Si cap layers were obtained. The density of Ag islands grown on the Si cap layer depends on its thickness. Factors contributing to this effect may include the average strain and Ge concentration on the surface of the Si cap layer. The effects of the Ag LSP on the PL of Ge coherent domes were investigated for both α-Si capped and bare Ag islands. For samples with low-doped substrates, the LSPs reduce the Ge dot-related PL when the Si cap layer is below some critical thickness and have no effect on the PL when the Si cap layer is above the critical thickness. For samples grown on highly-doped wafers, the LSP of bare Ag islands enhanced the PL of Ge QDs by ~ 40%. / Dissertation/Thesis / Doctoral Dissertation Physics 2015