Transmission electron microscopic and X-ray diffraction measurements were performed on multiple quantum-well structures which had been deposited onto (11•0) or (00•1) sapphire substrates. The multiple quantum-wells which were grown onto (11•0) substrates were still oriented along the (00•1) direction; due to an unusual growth mechanism. Transmission electron microscopic studies indicated that samples grown onto (11•0) sapphire substrates exhibited higher threading dislocation densities than did those grown onto (00•1) sapphire substrates. This was related to the initial growth stages of high-temperature GaN layers. Samples which were deposited onto (11•0) sapphire substrates exhibited a higher density of V-defects that incorporated a threading dislocation. Plan-view scanning electron microscopic images also showed that a higher density of small dark spots appeared in the paired form, as compared with that on (00•1) sapphire substrates. This generally corresponded to the presence of screw dislocations. It was recalled that V-defects and screw dislocations generally resulted in phase separation around such defects in InGaN, and finally gave rise to a strong exciton-localization effect.

A Study of Dislocations in InGaN/GaN Multiple Quantum-Well Structure Grown on (11•0) Sapphire Substrate. J.Bai, T.Wang, Y.Izumi, S.Sakai: Journal of Crystal Growth, 2001, 223[1-2], 61-8