Theory of the photon-drag effect inp-type germanium with a parabolic and anisotropic band-structure approximation

This paper shows that many features of the photon-drag voltage generated by illumination ofp-germanium with 10.6 μm radiation can be understood on the basis of a parabolic but anisotropic band-structure model. The group velocities of the heavy and light holes participating in the optical transitions are obtained by an analysis of the conservation laws. Since the nonequilibrium hole densities in both bands depend directly on the momentum relaxation times in the determinant equations of continuity, these times are the parameters with the strongest influence on the numerical results. The photon-drag voltage consists of components longitudinal and transverse with respect to the axis of illumination. For the longitudinal components, good agreement between our theoretical results and experimental data from the literature is achieved if the crystal is illuminated along a [100] or [111] direction. Though a transition probability independent of light polarisation has been assumed, the transverse effect (illumination along [111]) can be computed for special measuring conditions. The calculated effects of anisotropy are higher than known from experiments possibly due to the approximations used for the valence bands and the transition probability. An erratum to this article is available at .