Energy Band Structure of Gallium Antimonide

Abstract

Resistivity, Hall coefficient, and magnetoresistance were studied for n‐ and p‐type GaSb. The infrared absorption edge was investigated using relatively pure p‐type, degenerate n‐type, and compensated samples. Infrared absorption of carriers and the effect of carriers on the reflectivity were studied. The magnetoresistance as a function of Hall coefficient for n‐type samples at 4.2°K gave clear evidence for a second energy minimum lying above the edge of the conduction band; the energy separation is equal to the Fermi energy for a Hall coefficient of 5 cm³/coulomb. The shift of absorption edge in n‐type samples showed that the conduction band has a single valley at the edge, with a density‐of‐state mass m_d1=0.052 m. By combining the results on the edge shift, magnetoresistance, and Hall coefficient, it was possible to deduce: the density‐of‐states mass ratio m_d2/m_d1=17.3, the mobility ratio μ₂/μ₁=0.06, and the energy separation Δ=0.08 ev between the two sets of valleys at 4.2°K. Anisotropy of magnetoresistance, observed at 300°K, showed that the higher valleys are situated along (111) directions. The infrared reflectivity of n‐type samples can be used to deduce the anisotropy of the higher valleys; tentative estimates were obtained. Infrared reflectivity gave an estimate of 0.23 m for the effective mass of holes. The variation of Hall coefficient and transverse magnetoresistance with magnetic field and the infrared absorption spectrum of holes showed the presence of two types of holes. Appreciable anisotropy of magnetoresistance was observed in a p‐type sample, indicating that the heavy hole band is not isotropic; this was confirmed by the infrared absorption spectrum of holes. The results on the absorption edge in various samples seemed to indicate that the maximum of the valence band is not at k=0. However, it appears likely that transitions from impurity states near the valence band produced absorption beyond the threshold of direct transitions.