Study of GaN Crystals Growth on Patterned Sapphire Substrate by Hydride Vapor Phase Epitaxy Method
| Autor: | Hai-Ping Liu, 劉海平 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 In this dissertation, the hydride vapor phase epitaxy (HVPE) process and epitaxial lateral overgrowth (ELO) method were adopted to deposit the GaN thick films ( > 100 μm ) on patterned sapphire substrate (PSS) with control the growth temperatures in the range of 825 ℃ ~ 1050 ℃ and different carrier gas ratios (i.e. H2, N2, and N2/H2 ). The high temperature growth mode and low temperature nucleation mode were studied using H2 as a carrier gas. It is found that the formation mechanism of special GaN hexagonal columns at the low temperature of 850 ℃ is different from that of the high temperature GaN columns. Besides, the two step-growth method (i.e. low temperature from 850 ℃ to 900 ℃ and high temperature from 950 ℃ to 1050 ℃) is performed to control the growth rate of (0001) and {1-101} facets to reduce dislocation density by bending the threading dislocations and to increase thick film growth rate. Similar results by varying different carrier gas ratios (i.e. H2, N2, and N2/H2) are also shown to be effective in producing high quality thick epitaxial films with low threading dislocation density. The scanning electron microscopy (SEM) analysis was examined to observe the surface morphologies of GaN samples. The cathodoluminescence (CL) and Raman spectroscopy analyses were examined to detect luminescent spectra and local strain distribution, which can be associated with threading dislocation distribution by transmission electron microscopy (TEM) observation. X-ray rocking curves were examined to estimate GaN epitaxial quality and revealed that GaN samples grown in N2/H2 (147 arsec)or H2 (728 arsec) carrier gas are better than that grown in N2 (2913 arsec) carrier gas. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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