Radiative Recombination inn-Type InP

Photoluminescence spectra of relatively pure $n$-InP display several emission bands at low temperatures, with energy peaks near 1.41, 1.38, 1.34, and 1.30 eV. We report evidence that the 1.41-eV band is a direct recombination band, and that the 1.38-, 1.34-, and 1.30-eV bands are, respectively, a donor-acceptor recombination band and two weaker replicas displaced by one and two longitudinal optical phonons. With increasing temperature in the range from 50 to 70°K, the 1.38-eV band and its phonon replicas shift toward higher energy and are strongly quenched. We interpret the shift toward higher energy as due to an increasing importance of recombination of more closely spaced donor-acceptor pairs, and the quenching of the recombination band as due to increasing ionization of the donors. The dependence of the band peak energy on donor concentration agrees with the proposed process. In addition, we have studied the variation of the 1.38-eV band with excitation intensity. Saturation of this emission is observed at high intensities indicating an average lifetime of the order of ${10}^{-8\mathrm{}}$ sec at $n=7\mathrm{}\times {10}^{16}$ ${\mathrm{cm}}^3$. The 1.41-eV band becomes the dominant emission above 70°K. Its peak energy follows the gap variation with temperature from 2 to 300°K. It is independent of doping level and does not saturate with increasing excitation intensity. We believe that this band results from direct electron-hole recombination, and indeed the position and shape of the 1.41-eV band agree well with a calculation of the expected direct recombination emission. The calculation is based on detailed balance arguments and optical absorption data. Several other characteristics of the emission spectrum are discussed.