Recombination of carriers in SiGe/Si heterostructures measured by photomodulated intersubband absorption

Abstract

We used photoinduced absorption (PIA) spectroscopy of optical transitions between valence subbands of a nominally undoped SiGe/Si quantum wells to study the recombination processes of photogenerated carriers in these heterostructures. We measured the PIA as a function of the ambient temperature, photo-excitation density and modulation frequency. Our measurements show that the recombination kinetics is governed by both an extrinsic mono-molecular and intrinsic bi-molecular terms. We account for this density dependence by a simple rate model which takes into account thermal activation of the photogenerated holes out of the SiGe wells. The model describes very well the measured temperature dependence of the PIA and it provides quite an accurate determination of the intrinsic recombination rate of electrons and holes within the well regions in these heterostructures. The rate that we obtain is faster than the measured recombination rates in bulk Si and Ge. This recombination rate enhancement is possibly due to carriers confinement within the SiGe well regions.