INFLUENCE OF AS AUTODOPING FROM GAAS SUBSTRATES ON THICK CUBIC GAN GROWTH BY HALIDE VAPOR-PHASE EPITAXY

GaN layers were grown on (001) GaAs substrates by halide vapor phase e pitaxy (HVPE) on either a high-quality cubic buffer layer grown by met alorganic molecular beam epitaxy (MOMBE) or a HVPE buffer layer on bot h sides of the substrate. Though a high-quality cubic GaN (cubic compo nent : more than 99% for 2 mu m thick layer) was grown on the MOMBE bu ffer layer, the photoluminescence intensity was less than that of the layer grown on the HVPE buffer layer by about two orders of magnitude. This was found to be due to arsenic (As) autodoping from the back sid e of the GaAs substrate. The As autodoping decreased the optimum growt h temperature of cubic GaN by about 50 degrees C. The hexagonal compon ent increased with an increase in the growth thickness, independent of the initial cubic purity of the grown layer, suggesting that influenc e of the As autodoping decreased with an increase in the growth thickn ess.