Temperature-Dependent Radiative Recombination Mechanisms in GaP (Zn,O) and GaP (Cd,O)

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Abstract
Henry et al. have shown that the low-temperature red luminescence in both GaP(Zn,O) and GaP(Cd,O) is composed of a bound-exciton band overlapped at lower energies by a new type of long-lived pair band. This paper describes a study of the temperature dependence of the spectral positions and time-decay characteristics of these red bands. The samples were excited with electrons from a pulsed accelerator, and the bands were studied by time-resolved spectroscopy in the range 1.7-300°K. At low temperatures the intensity ratio of the pair and bound-exciton bands is dependent upon sample preparation and excitation intensity. Regardless of the initial value of the ratio, the exciton emission becomes dominant in a transitional temperature range between 60 and 120°K. At room temperature the emission is almost entirely excitonic. The accompanying large changes in the spectral and time-decay characteristics are semiquantitatively explained by a theory based on the assumption of thermal equilibrium of holes amongst the exciton-hole, acceptor, and valence-band states. Luminescence excitation measurements in GaP(Zn,O) were used to estimate the concentrations of Zn-O complexes which were correlated with relative luminescence efficiencies and melt compositions.