Alternative Microstructure of GaN Nucleation Layers Grown by Low Pressure Metal-Organic Vapor Phase Epitaxy on Sapphire Substrate
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- Category: Tungsten & Sapphire Growth Furnace News
- Published on Thursday, 23 January 2014 11:21
Predominately hexagonal GaN nucleation layers were grown on sapphire substrate by low pressure metal-organic vapor phase epitaxy. Tilt angles of GaN single crystallites about the normal of sapphire substrate are determined to be in the range from 0° to 5° by using selected area electron diffraction. A small portion of cubic phase of GaN was observed to be selectively distributed in the grain boundary areas and the instantaneous surface state is suggested to play an important role in the nucleation of the Zincblende phase. Phase transition from hexagonal to cubic GaN caused by heavy radiation from ion beam was also noticed. A critical temperature is proposed to exist in forming predominately cubic or hexagonal GaN nucleation layer.
We studied the effects of the growth rate of a GaN buffer layer grown on a GaN epilayer. It was found that this growth rate plays a key role in improving the quality of the GaN film on a sapphire substrate and an optimum growth rate exists that yields the best crystal quality. A GaN film grown on a buffer layer with the optimum growth rate of 18.3 nm/min has an electron Hall mobility of 539 cm2/V s and a dislocation density of approximately 2×108 cm-2. These improvements of GaN film qualities are illustrated by the promotion of the lateral growth mode.
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