Light emission from forward biased p-n junctions in gallium phosphide

Abstract

Deep recombination centers in homogeneously doped and as-grown single crystals of GaP have been studied by Hall effect, photoluminescence and absorption spectra. These centers act as radiative recombination centers for injected carriers in forward-biased p-n junctions doped with the same impurities. One of these levels, a deep donor, 0·4 eV below the conduction band, is present in most of the undoped crystals and is very likely associated with substitutional oxygen as a residual impurity in the 1–5 × 10 18 atoms/cm 3 range. In several specific cases this center determines the rate of recombination of minority carriers in the junction transition region. The non-radiative decay from this level in comparison with the radiative lifetime of the center (10 −5 sec) determines the quantum efficiency of the luminescent process (10 −2 at 80°K) and the light-emission decay time (10 −8 sec at 300°K). Other deep radiative recombination centers are due to impurities (S, Se, Te, Cu, Zn, Mg and Cd) which have interacted with the deep-donor center. Their effect upon the luminescent processes has been correlated with an equilibrium between substitutional oxygen and interstitial oxygen. A third type of emission giving rise to fairly narrow lines (0·01 eV at 20°K) is most probably due to molecular aggregates of interstitial oxygen with host lattice atoms. Finally, direct band-to-band recombination luminescence is observed, although it is relatively inefficient (10 −8 at 300°K).