Absorption saturation of heavy- to light-hole band transitions in p-type InSb.

Abstract

We present calculations of the intensity dependence of the free-hole absorption coefficient in p-type indium antimonide for high-intensity light with a wavelength near 10 \ensuremath{\mu}m. The dominant absorption mechanism is direct inter-valence-band transitions, where a hole occupying a state in the heavy-hole band makes a direct transition to a state in the light-hole band. The absorption coefficient due to this mechanism is predicted to decrease with increasing intensity in a manner closely approximated by an inhomogeneously broadened two-level model. Values for the saturation intensity ${I}_{S}$ are reported as a function of the photon energy, lattice temperature, and hole density. The dependence of ${I}_{S}$ on the hole concentration allows considerable tunability of the saturation behavior, so that for a fixed laser intensity, the degree of absorption saturation can be adjusted by controlling the doping density of the sample. For lightly doped samples at a temperature of 77 K, the free-hole absorption begins to saturate at intensities of less than 10 kW/${\mathrm{cm}}^{2}$, which is between one and two orders of magnitude smaller than the intensities required to saturate the comparable transitions in Ge and GaAs. The calculated results are also important to measurements of the two-photon absorption coefficient ${K}_{2}$ in InSb, and they indicate that much of the transmission data used to obtain a value for ${K}_{2}$ must be reevaluated.