Infrared Absorption and Valence Band in Indium Antimonide

Infrared absorption is studied at near liquid helium temperature for $n$- and $p$-type degenerate samples of various carrier concentrations. The absorption in $p$-type samples, at photon energies larger than the energy gap, depends on the hole concentration. The results show that the valence band is warped and that the energy at $k=0\mathrm{}$ is very close to the maximum energy of the band. A step in the absorption of $n$-type samples is observed which gives an estimate of $\sim 0.012m$ for the effective mass of light holes. The long wavelength absorption in $p$-type samples is characteristic of intervalence band transitions.