Columnar Structures and Stress Relaxation in Thick GaN Films Grown on Sapphire by HVPE
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Abstract
Thick GaN films with high quality are directly grown on sapphire in a home-built vertical hydride vapour phase epitaxy (HVPE) reactor. The optical and structural properties of large scale columnar domains near the interface are studied using cathodoluminescence and micro-Raman scattering. These columnar domains show a strong emission intensity due to extremely high free carrier concentration up to 2×1019cm-3, which are related with impurities trapped in structural defects. The compressive stress in GaN film clearly decreases with increasing distance from interface. The quasi-continuous columnar domains play an important role in the stress relaxation for the upper high quality layer.
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