Hole-phonon scattering in strained SiGe quantum wells

The interaction between holes confined in a strained Si _1-xGe_x quantum well and acoustic and optical phonons is investigated in an effort to elucidate in-plane carrier transport. This treatment utilizes conventional deformation potential theory within the context of the momentum conservation approximation in the confinement direction to obtain analytical expressions for both acoustic and optical phonon scattering rates as functions of carrier energy. The optical phonon interaction explicitly accounts for the three vibrational modes: Si-Si, Si-Ge, and Ge-Ge by incorporating experimentally determined longitudinal optical (LO) phonon frequency shifts in the calculation of the matrix elements. The oscillator strengths for each of these LO (short wavelength) modes are approximated using a binomial distribution to describe the local atomic arrangement of a unit cell. The two-dimensional scattering rates are evaluated and compared with bulk scattering calculations for a well of fixed width and varying Ge content. It is found that the overall hole-phonon scattering rate in a SiGe well is higher than that of holes in strained SiGe layers due to the combined effects of similar two- and three-dimensional density of states and large inter-sub-band scattering. A qualitative description of high field transport within the well is obtained by calculating the relative contributions of particular optical phonon modes to the overall scattering rate at high carrier energies.