Author: Bei-Shen SywePublisher:
ISBN:
Category :
Languages : en
Pages : 302
Book Description
Epitaxial Growth of Layered Structures of Silicon Carbide and Aluminum Nitride by Metal-organic Chemical Vapor Deposition
Author: Bei-Shen SyweAluminum Nitride Buffer Layer Growth for Group III-nitride Epitaxy on (111) Silicon
Author: Andrew Philip LangePublisher:
ISBN: 9781369615760
Category :
Languages : en
Pages :
Book Description
This dissertation examines the growth of aluminum nitride (AlN) on (111) silicon by metalorganic chemical vapor deposition. AlN is commonly used as a buffer layer for the growth of gallium nitride on silicon templates. This makes the development of growth protocols for high quality, smooth AlN films on silicon critical to improving the performance and reliability of III-nitride on silicon devices such as light emitting diodes and high power transistors. The optimal nucleation conditions for AlN on silicon have been heavily disputed. Some crystal growers expose the substrate to aluminum prior to AlN deposition, which has been shown to improve crystal quality and decrease surface roughness of both AlN buffer layers and overgrown gallium nitride. However, others adopt an ammonia-first approach, in which the substrate is nitrided prior to AlN deposition. Both can be effective depending on the growth conditions, which has resulted in considerable controversy regarding how aluminum, nitrogen, and silicon interact during these initial "predoses" and how the resulting morphology influences subsequent AlN and gallium nitride growth. The structure and morphology of aluminum predose layers deposited directly on (111) silicon at ~970 °C both with and without subsequent ammonia exposure were studied using electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Three morphological features were identified -- trenches, islands, and patches. When the predose layer was not exposed to ammonia, a roughening of the substrate was observed, similar to what occurs when gallium reacts with silicon. This gave rise to aluminum rich surface trenches, which suggests that silicon is dissolved by liquid aluminum and the resulting aluminum-silicon liquid solution evaporates. When the predose layer was exposed to ammonia, faceted patches were observed with small islands near their edges. The islands were composed of both zinc-blende and wurtzite AlN polytypes, while the patches consisted of diamond cubic silicon with dilute concentrations of aluminum. A model was proposed to explain these features in which the liquid aluminum-silicon surface layer is converted into AlN and silicon upon nitridation. Low temperature and high temperature AlN growth was examined after varied aluminum predoses using electron microscopy and atomic force microscopy with the aim of explaining anomalous AlN-silicon interface structures observed by others. AlN formed small, three-dimensional islands when grown directly on the substrate at ~970 °C with no predose. When the substrate was first exposed to a predose at ~970 °C, AlN nucleated on both island and patch features causing them to grow laterally and eventually coalesce. The morphologies of films grown with and without predoses were nearly identical after coalescence. This suggests that growth at this temperature is kinetically limited and does not depend on the nucleation surface. At high temperatures (~1060 °C), enhanced lateral growth on patch features formed during the predose was observed. The AlN-silicon interface was found to be predominantly amorphous when no predose was used, consistent with previous reports. The interface was structurally abrupt when aluminum was deposited prior to growth, but contained an additional phase consistent with the zinc-blende islands observed in predose layers. It was proposed that the amorphous SiN[subscript x] interfacial layer formed between nucleation sites when no predose was used as the substrate was exposed to an ammonia ambient prior to lateral growth of the nuclei. When the substrate was first exposed to a predose, aluminum rich silicon patches covered the surface. The presence of aluminum in the patches may limit the reaction between silicon and nitrogen during the early stages of growth. Dislocations in buffer layers grown both with and without aluminum predoses were studied using weak beam dark field transmission electron microscopy. A mosaic microstructure was observed which consisted of clustered dislocations along subgrain boundaries. Many of these subgrains were not bounded by dislocations on all sides, which suggests they did not form by the coalescence of misaligned islands. It was proposed they formed instead by the clustering of dislocations due to attractive and repulsive interactions. Dislocation densities were lower in films grown with a predose, which resulted in the formation of fewer subgrains. It was also found that buffers grown with a predose had a smoother surface. The surface of buffer layers grown without a predose contained small pits along the edges of surface terraces. The separation and geometry of these terraces was consistent with the subgrain structure, indicating surface step bunching may occur around subgrains where dislocation densities are high. Consistent with III-nitride growth on alternative substrates, a-type threading dislocations with line directions normal to the basal plane were found to terminate within highly defective, low temperature nucleation layers. C-type threading dislocations were found to terminate near the AlN-Si interface. It was suggested that the former originate from the climb of basal plane dislocations which form through the dissociation of Shockley partials or the coalescence of I1 type stacking faults. It was suggested that the latter nucleate from surface steps on the substrate. The observed improvement in crystal quality of buffer layers grown with a predose may be due to dislocation annihilation events, rather than the nucleation of fewer threading dislocations. This is corroborated by the presence of voids in the substrate when the buffer was grown with a predose, which indicates that point defects diffuse across the abrupt interface during growth. The presence of amorphous interfaces in films grown without an aluminum predose may inhibit the diffusion of point defects and thereby deter dislocation climb. If this mechanism is active as evidence in this dissertation suggests, an appropriate objective of any nucleation process for AlN buffer layers on silicon may be to improve the structural coherence of the interface.
Growth of Single Crystalline Silicon Carbide on Aluminum Nitride by Chemical Vapor Deposition
Author: Payam ShoghiPublisher:
ISBN:
Category :
Languages : en
Pages : 154
Book Description
Crystalline layers of SiC were grown on A1N substrate using chemical vapor deposition (CVD) from a single gas source; Trimethylsilane as well as a combination of ethylene (C[subscript]2H[subscript]4), silane (SiH[subscript]4), and hydrogen (H[subscript]2) gas. The growth was conducted at temperatures ranging from 1100 to 1350[degrees]C and pressures ranging from 0.09 torr to l.86 torr. The study was conducted on AlN grown on sapphire as well as on polycrystalline AlN substrates. The CVD growth system, which was made by OSEMI, was designed to operate in wide range of pressures (10[superscript]-8 to atmospheric) and temperatures (room temperature to -2000[degrees]C) using RF heating. The system is integrated with a molecular beam epitaxy (MBE) unit to enable direct transfer of A1N layers, grown by MBE, into the CVD system. X-ray measurements, carried out using PANalytical X'Pert X-ray diffraction system demonstrated growth of single crystalline SiC while surface morphology was examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM), qualitative measure of the layers' stoichiometry was carried out using Energy Dispersive X-ray examination using conventional EDAX. The formation of single crystalline 3C-SiC was confirmed by X-ray diffraction. Atomic force microscopy (AFM) showed an increase in the roughness of the morphology for thick cubic SiC on A1N on Sapphire substrate. SEM and EDAX measurements showed the thickness of the SiC thin film and the ratio of Si and C atoms in the film.
Dissertation Abstracts International
Author: Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 806
Book Description
Scientific and Technical Aerospace Reports
Author: Electrical & Electronics Abstracts
Author: Publisher:
ISBN:
Category : Electrical engineering
Languages : en
Pages : 2240
Book Description
Silicon Carbide and Related Materials, Proceedings of the Fifth Conference, 1-3 November 1993, Washington DC, USA
Author: Michael G. SpencerPublisher: CRC Press
ISBN:
Category : Art
Languages : en
Pages : 768
Book Description
USA companies working in this area include Westinghouse. This material is being investigated primarily in the USA, Japan and Russia alongside that into wide-gap compounds which feature similar characteristics. Applications include high temperature ultra-violet lasers, photodiodes, photodetectors, blue LEDs, high power microwave applications in radar and transmitter devices Special sale to delegates 200 @ 35 Previous volumes in series published by Springer Leading workers in field include Pavlidis (MIT) and Choyke (Pittsburgh, Dept Phys) Feng author is also presenting paper Research in this area is expanding
Metalorganic Chemical Vapor Deposition of Aluminum Nitride and Aluminum Nitride/silicon Carbide Solid Solutions
Author: I. WangThe Journal of the Korean Physical Society
Author: Chemical Vapor Deposition: 1960-1980
Author: Donald T. HawkinsPublisher: Springer
ISBN:
Category : Reference
Languages : en
Pages : 762
Book Description