Light-hole to heavy-hole acoustic phonon scattering rate

A superlattice consisting of periods of 90 Angstrom Si0.7Ge0.3 quantum well s and 50 Angstrom Si barriers on a (100) Si0.81Ge0.19 buffer is investigate d for the purpose of designing Si-based terahertz intersubband lasers using the feature of inverted light-hole effective mass. It has been shown that the energy subband dispersion curve of this structure demonstrates a region of inverted light-hole effective mass. Since the energy separation between the two lowest subbands that are also of different type is below the optic al phonon energy, acoustic phonon scattering is an important nonradiative p rocess and is therefore studied. Our result indicates that the intersubband phonon scattering process is much weaker between different types of subban d. For the particular structure of interest, this scattering rate is about 0.5/ns, corresponding to an intersubband lifetime of 2 ns, which is much lo nger than the typical lifetime of 1 ps when it is between subbands of the s ame kind.