The effect of the growth temperature and of heat treatments upon the luminescence properties of heterostructures that had been grown by rapid thermal chemical vapor deposition was studied. Excitonic luminescence of the strained SiGe layers was observed in samples which were grown at temperatures above 700C, but the signal completely disappeared for deposition temperatures of less than 650C. After rapid thermal annealing, a marked improvement in the luminescence efficiency of layers which had been deposited at low temperatures was detected. A blue-shift of the excitonic luminescence was also observed, and was explained in terms of the interdiffusion of Si and Ge during heating. The photoluminescence spectra, after rapid thermal annealing at 1050C, were used to make a study of the thermal stability of strained Si0.85Ge0.15. It was shown that, when the layers were in a metastable state before annealing, relaxation led to a photoluminescence signal which consisted of both band-edge and dislocation-related recombination. In this case, strain relaxation was attributed mainly to the formation of misfit dislocations at the SiGe/Si hetero-interface. In very thin SiGe layers, only the band-edge luminescence could be observed. It shifted to the high-energy side, as predicted by the interdiffusion model. By using a simple theoretical approach, this shift could be used to calculate the interdiffusion coefficient. Good agreement was found with published data.

A.Souifi, T.Benyattou, G.Guillot, G.Brémond, D.Dutartre, P.Warren: Journal of Applied Physics, 1995, 78[6], 4039-45