ABOVE-BAND-GAP PHOTOLUMINESCENCE FROM N-TYPE CDTE .1. GROWN BY MOLECULAR-BEAM EPITAXY

We report the observation of above-band-gap radiative recombination from highly doped n-type CdTe:I epilayers grown by molecular-beam epitaxy. Radiative emission involving phonon absorption processes was observed at sample temperatures up to 30 K with excitation power densities as low as 300 mW/cm2 using conventional phase-sensitive signal detection. The momentum-conserving phonon absorption photoluminescence (PL) process in the epilayers involves excitons with an average kinetic energy of 5 meV. Even though phonon emission bands of donor-related recombination have not been observed in CdTe, we see a clear indication of phonon absorption PL due to coupling with donor states. The dependence of PL intensity on incident excitation power density for near-band-edge and above-band-gap emissions reveals that phonon absorption processes increase at a slightly faster rate, indicative of the strong electron-phonon coupling in CdTe.