The effect of the growth parameters upon the optical quality of InGaN which had been grown onto GaN was investigated. The photoluminescence spectrum of a sample with a low-temperature grown GaN cap layer, or a graded-temperature grown GaN cap layer, exhibited a shorter peak wavelength than that of a sample which had a GaN layer that had been grown at normal temperatures. The shift in the peak wavelength increased, with increasing layer thickness, for samples with caps that had been grown at low temperatures. This was because the defects that were present in a cap layer which had been grown at low temperatures encouraged the out-diffusion of In atoms during temperature ramping. The narrower line-widths and higher intensities of the photoluminescence spectra of InGaN after In out-diffusion were attributed to a reduction in strain, or in the dislocation or defect contents. The Raman and Auger electron spectra also indicated that GaN which was grown at low temperatures contained a lot of defects. This reduced the phonon peak intensity, and led to the interdiffusion of In atoms during the growth of GaN/InGaN heterostructures.

J.S.Tsang, J.D.Guo, S.H.Chan, M.S.Feng, C.Y.Chang: Japanese Journal of Applied Physics - 1, 1997, 36[3B], 1728-32