Hole scattering mechanisms in Hg1−xCdxTe

Abstract

In this paper, we analyze and discuss the roles of nine different scattering mechanisms—ionized impurity, polar and nonpolar optical, acoustic, dislocation, strain field, alloy disorder, neutral impurity, and piezoelectric—in limiting the hole mobilities in p-type Hg1−xCdxTe crystals. The analysis is based on obtaining a good fit between theory and experiment for the light and heavy hole drift mobilities by optimizing certain unknown (or at the most vaguely known) material parameters such as the heavy hole mobility effective mass, degree of compensation, and the dislocation and strain field scattering strengths. For theoretical calculations, we have adopted the relaxation time approach, keeping in view its inadequacy for the polar scattering. The energy dispersive hole relaxation times have been drawn from the published literature that take into account the p-symmetry of valence band wave functions. The temperature dependencies of multiple charge states of impurities and of Debye screening length have been taken into account through a numerical calculation for the Fermi energy. Mobility data for the present analysis have been selected from the HgCdTe literature to represent a wide range of material characteristics (x=0.2–0.4, p=3×1015–1×1017 cm−3 at 77K, μpeak≅200-1000cm2V−1s−1). While analyzing the light hole mobility, the acoustic deformation and neutral impurity potentials were also treated as adjustable. We conclude that • the heavy hole mobility is largely governed by the ionized impurity scattering, unless the strain field or dislocation scattering below 50K, or the polar scattering above 200K, become dominant; • the light hole mobility is mainly governed by the acoustic phonon scattering, except at temperatures below 30K where the neutral impurity, strain field and dislocation scattering also become significant; • the intervalence scattering transitions make negligible impact on the heavy hole mobility, but virtually limit the light hole mobility; • the alloy disorder scattering does not dominate in any temperature region, although it exercises some influence at intermediate temperatures; • the heavy hole mobility effective mass ratio mhh/mo∼-0.28–0.33 for crystals with x<0.4; and • the light hole band deformation potential constant is ∼12 eV.