Infrared Spectral Emittance of InAs

The infrared absorption spectra for a $p$-type InAs sample were determined by measuring the spectral emittance at 77, 203, and 373°K. The spectra contained features which are identified with optical edge transitions, free-carrier absorption, intervalence-band transitions, multiphonon absorption and the reststrahlen band. The two-phonon spectra are analyzed in detail. Using selection rules, assignments at the critical points $\Gamma$, $L$, and $X$ are given for the optical and acoustical modes. It is found that the "sum rule" for lattice modes is in good agreement with the assignments.