Recombination Radiation from InSb

Abstract

The recombination radiation spectra of a variety of $n$- and $p$-type InSb single crystals were experimentally investigated at 300, 200, 100, and 12°K using radiation from a zirconium arc source as the generator of excess carriers. The emission spectra included contributions from direct band-to-band transitions, indirect phonon-assisted band-to-band transitions, transitions to flaws, and transitions between localized states not thermally coupled to the lattice, the transition energies of which were larger than the band gap of InSb. The direct band-to-band line, generally the major component, is in good agreement with the band model of this semiconductor. The room-temperature emission and radiative lifetime agree very well with those predicted by small-signal statistical theory. At 12°K a line at 0.215 eV is a result of an indirect band-to-band transition involving the emission of an optical phonon. Other lines in the 12°K spectra are correlated with the presence of zinc (0.228 eV), silver (0.209 and 0.186 eV), and gold (0.193 eV) as impurities. The energies of these emission lines indicate that at low concentrations the zinc level is 0.010 eV above the valence band, the two silver levels are located 0.027 eV and 0.050 eV above the valence band, and the lowest gold level is 0.043 eV above the valence band. One other line having no apparent relation to an impurity was observed at 0.225 eV. Emission from a highly impure $n$-type crystal revealed a decrease of the band gap due to the extension of the density-of-states below the intrinsic conduction band minimum and a rigid shift of the bands. Comparison of this experimental distribution with those calculated for band-to-band and band-to-flaw transitions from a filled band with and without k conservation indicate that in this case the emission is probably due to direct, non-k-conserving transitions. Narrow ($<\mathrm{kT}$), low-intensity lines were superimposed upon the direct band-to-band radiative recombination photon distribution. Close to the energy of the band gap, these lines were equally spaced in energy (at about 0.010 eV). At higher energies the energy separation of these lines increased. The existence of these lines appears to be related to the concentration of electrons in the conduction band.