THE LONG-TERM RELAXATION AND BUILDUP TRANSIENT OF PHOTOCONDUCTIVITY IN SI1-XGEX/SI QUANTUM-WELLS

The long-term relaxation and build-up transient of photoconductivity has been observed in Si1-xGex/Si quantum wells. The long-term relaxation behaviour pelt) of photoconductivity can be described by a stretched-exponential function, I-pc(t) = I-pc(0) exp[-(t/tau)(beta)] (0<i beta <1) for T < 160 K, which is usually observed in a wide class of disordered materials. The long-term build-up transient of photoconductivity has been measured and formulated at different temperatures, which also indicates the existence of the band-tail states due to alloy disorder. The distribution of tail states has been confirmed to be exponential in energy. Our results suggest that the alloy potential fluctuations induced by compositional fluctuations can strongly influence the transport as well as optical properties of Si1-xGex/Si quantum wells.