Molecular-beam epitaxially grown highly strained Ga0.65In0.35As/GaAs multiple quantum-well structures were investigated. Interdiffusion was carried out via rapid thermal annealing, at temperatures of between 700 and 950C, by using GaAs proximity caps and electron-beam evaporated SiO2 cap layers, respectively. Reduced photoluminescence line-widths and increased photoluminescence intensities were observed after diffusion-induced band-gap shifts that ranged from 0.006 to 0.220eV. Microscopic photoluminescence methods were used to study the onset of strain relaxation due to dislocation generation. Two types of line defect were found in samples which had been annealed using proximity caps; depending upon the annealing temperature and the number of quantum wells. These were misfit dislocations with their lines parallel to <110> directions, and <100>-oriented line defects. No dislocations were observed, in samples which had been annealed using a SiO2 cap, over the entire temperature range which was investigated here. Resonant Raman scattering measurements of the 1LO/2LO phonon intensity ratio were used to make semi-quantitative assessments of the total defect content; including point defects. It was found that, whereas increasing point defect densities, and the formation of line defects, were observed in proximity-capped samples as the annealing temperature was increased, no deterioration of structural quality due to an increased point defect density was observed in samples which had been annealed using a SiO2 cap.

S.Bürkner, M.Baeumler, J.Wagner, E.C.Larkins, W.Rothemund, J.D.Ralston: Journal of Applied Physics, 1996, 79[9], 6818-25