EFFECT OF RAPID THERMAL ANNEALING ON THE PHOTOLUMINESCENCE PROPERTIES OF SIGE/SI HETEROSTRUCTURES

The effect of growth temperature and thermal treatments on the luminescence properties of SiGe/Si heterostructures grown by rapid thermal chemical-vapor deposition is reported. While the excitonic luminescence of the strained Si1-xGex layer is observed in the samples grown above 700 degrees C, the signal completely disappears for deposition temperatures lower than 650 degrees C. After rapid thermal annealing, we show that a drastic improvement of the luminescence efficiency of the layers deposited at low temperatures is obtained. A spectral blue shift of the excitonic luminescence can also be observed and is interpreted in terms of interdiffusion of Si and Ge atoms during the heating process. The photoluminescence spectra after a rapid thermal annealing at 1050 degrees C have been used for the first time to perform an accurate study of the thermal stability of strained Si0.85Ge0.15 alloys. It is shown that when the layers are in a metastable state before annealing, the relaxation phenomenon leads to a photoluminescence signal which consists of both band-edge and dislocation-related recombinations. In this case, the strain relaxation is mainly attributed to the formation of misfit dislocations at the SiGe/Si heterointerface. In very thin SiGe layers, only the band-edge luminescence can be observed, but it is shifted to the high-energy side as expected by the interdiffusion model. Using a simple theoretical approach, this shift can be used to calculate the interdiffusion coefficient in good agreement with the literature data. (C) 1995 American Institute of Physics.