Low Temperature Growth Mechanism of GaN Crystal by Hydride Vapor Phase Epitaxy
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Low Temperature Growth Mechanism of GaN Crystal by Hydride Vapor Phase Epitaxy (a) (a,*) Hai-Ping Liu , In-Gann Chen , Jenq-Dar Tsay(b), Wen-Yueh Liu(b), Yih-Der Guo(b), Jung Tsung Hsu(b) (a) Department of Material Science and Engineering, National Cheng-Kung University, Tainan, Taiwan, ROC (b) Opto-Electronics & System Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan, ROC ABSTRACT The low temperature growth of GaN crystal using epitaxy lateral overgrowth (ELO) on SiO2 dot pattern below 900 by hydride vapor phase epitaxy (HVPE) have been studied. It is observed that the growth rate of GaN hexagonal pyramidal crystals along [1 1 01] direction increases as growth temperature decreases. At low temperature of ~ 850, hexagonal GaN columnar crystals with high index facet at the top can be observed. It is proposed that the surface diffusion length of precursors, such as NH3 and GaCl, decreases at lower temperature that reduces the probability of desorption and increase the lifetime. The condensation of Ga liquid droplets on the GaN surface will change the relative stability of {1 1 01} facet. Therefore, the formation of high index planes such as {1122} facet on the top of hexagonal column along with the formation of stacking fault on the (0001) plane can be observed. A detailed study of the effect of growth temperature on the crystal growth mechanism will be presented. Keywords: GaN, HVPE, hexagonal columns Corresponding author
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INTRODUCTION GaN is a wide-band gap semiconducting compound (3.4 eV) that makes it suitable for optoelectrical applications in the spectral range from blue to ultraviolet [1-2] and in high-power/high-temperature transistors. As a result of large lattice mismatch between GaN and sapphire substrate, many studies have been conducted to synthesize low defects GaN wafer in order to produce device with high efficiency. It was shown that two-step metalorganic vapor phase epitaxy (MOVPE) process and epitaxy lateral overgrowth (ELO) [3-4] can reduce GaN threading dislocations grown on hetero-substrate, such as sapphire or silicon carbide. There have been several attempts to prepare bulk GaN crystals, such as solution growth under ultra-high nitrogen pressure [5] or sublimation method [6], but the size of GaN crystals obtained by these methods are too small for practical use.
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Several studies have been investigated in growing thick GaN films up to hundreds of m with low threading dislocations by hydride vapor phase epitaxy (HVPE) on hetero-substrates such as sapphire [7-8] and GaAs [9]. These GaN thick films can then be separated from the hetero-substrate and used as a substrate. The GaN substrate grown by HVPE is an attractive method due to its low cost and high growth rate. It was also reported that the GaN surface is smooth
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