GaN layers were grown on (001) GaAs substrates by hydride vapor phase
epitaxy (HVPE) with buffer layers grown by HVPE under various growth c
onditions. The ratio of cubic to hexagonal components in the grown GaN
layers was estimated from the ratio of the integrated X-ray diffracti
on intensities of the cubic (002) and hexagonal (10 (1) over bar 1) pl
anes measured by omega scan. It was found that the cubic/hexagonal rat
io greatly depended on the thermal cleaning prior to the buffer layer
growth and growth conditions. A thick GaN layer whose cubic component
was more than 85% was obtained with thermal cleaning at 600 degrees C
for 10 minutes, a similar to 30 nm buffer layer grown at 500 degrees C
and a V/III ratio of 300 during growth at 800 degrees C.