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

The effect of growth temperature and thermal treatments on the lumines cence properties of SiGe/Si heterostructures grown by rapid thermal ch emical-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 tempera tures lower than 650 degrees C. After rapid thermal annealing, we show that a drastic improvement of the luminescence efficiency of the laye rs 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 105 0 degrees C have been used for the first time to perform an accurate s tudy of the thermal stability of strained Si0.85Ge0.15 alloys. It is s hown that when the layers are in a metastable state before annealing, the relaxation phenomenon leads to a photoluminescence signal which co nsists of both band-edge and dislocation-related recombinations. In th is case, the strain relaxation is mainly attributed to the formation o f misfit dislocations at the SiGe/Si heterointerface. In very thin SiG e layers, only the band-edge luminescence can be observed, but it is s hifted to the high-energy side as expected by the interdiffusion model . Using a simple theoretical approach, this shift can be used to calcu late the interdiffusion coefficient in good agreement with the literat ure data. (C) 1995 American Institute of Physics.