Optical characterization of indium arsenide antimonide semiconductors grown by molecular beam epitaxy

InAs{dollar}rmsb{lcub}1-x{rcub}Sbsb{lcub}x{rcub}{dollar} is an attractive material for optoelectronic devices because it provides the lowest direct energy gap of the III-V semiconductors. Undoped, MBE-grown InAs{dollar}rmsb{lcub}1-x{rcub}Sbsb{lcub}x{rcub}{dollar} nearly lattice-matched to (100) GaSb substrates ({dollar}-{dollar}0.617% {dollar}leq Delta{dollar}a/a {dollar}leq{dollar} +0.708%) was studied by optical characterization to determine its material parameters and crystalline quality. Absorption measurements at temperatures between 6-295 K determined the energy gap and wavelength-dependent absorption coefficient for each sample. The resulting compositional dependence of the energy gap was anomalous when compared to previously reported data, suggesting that phase separation existed in this material. The samples were also studied by temperature- and excitation-dependent photoluminescence (PL), which resulted in single-peaked spectra for the majority of cases; this peak was identified as band-to-band recombination by comparison with absorption data. Linewidths as narrow as 4.3 meV and the observation of LO-phonon replicas both indicated high material quality, but the shift of the band edge peak to higher energies with increased excitation was much greater than expected from band filling alone and underscored the likelihood of phase separation. Additional extrinsic PL peaks were also observed from one of the undoped samples, and were identified as a free-to-bound transition at 4-7 meV and a donor-acceptor pair transition at 10-14 meV below the band edge. Characterization of ion implanted and epitaxially doped InAs{dollar}rmsb{lcub}1-x{rcub}Sbsb{lcub}x{rcub}{dollar}:Be identified the Be acceptor energy as {dollar}>{dollar}30 meV above the valence band in this material.