Thermal relaxation processes in Si_1-xGe_x/Si quantum wells studied by inter-subband and inter-valence band spectroscopy

In this paper we present a systematic experimental investigation of the optical properties associated with inter-subband and inter-valence band transitions in p-type pseudomorphic Si_1-xGe_x/Si multiple quantum-wells structure under high-temperature thermal treatments. The structure exhibits two types of optical absorption lines: the first obeys the inter-subband selection rules and is assigned to heavy-hole transitions while the second obeys the inter-valence band selection rules and is assigned to transitions between a heavy hole and a mixed spin split off and light-hole state. Annealing treatments reveal two kinds of thermally activated processes. The first process is assigned to strain relaxation while the second is assigned to Si and Ge inter-diffusion. Raman spectroscopy provides additional support to our interpretation of the activation processes. We propose a quantitative model, based on the Bir-Pikus deformation potential to explain the experimental results.