Energy and momentum relaxation of charge carriers in Ge and Si under uniaxial stress

Measurements of the piezoresistance and the energy relaxation time T_?, in Ge and Si under uniaxial stress up to 4 kb are reported in the temperature range 30 K < T < 300 K. The measurements of t_? have been performed in the warm carrier range using the harmonic mixing technique. The experimental results for the piezoresistance and energy relaxation time in n-type material can roughly be understood in terms of carrier redistribution in the conduction band valleys whose degeneracy is lifted by the stress. Information is obtained from these measurements about the relative strength of ? and g type intervalley scattering in n-Si; we find nearly equal coupling strength for both scattering types. For the p-type material the experiments show convincingly that the main effect of stress on transport quantities is also caused by the lifted degeneracy of the heavy and light hole bands, as predicted already by Adams, and by Pikus and Bir. The nonlinear dependence of the piezoresistance and τ_? on the stress can very well be explained by approximating the heavy and light hole bands as spherical and parabolical and using the deformation potential constant b as a parameter. The value of ≈2eV obtained for |b| is in good agreement with earlier results for p-Ge.