Abstract

Two basic characteristics of localized excitons in GaAs_1−xP_x are depicted in this study. They are: (1) the density of state extends into the band gap, and (2) the effective range of the wave-function is a sensitive function of its binding energy.¹ The photoluminescence (PL) properties of the ${\text{M}}_0^{\text{X}}$ band in indirect gap GaAs_1−xP_x has been reported.^2,3 The origin of the Mg band has been attributed to the exciton localized by the potential fluctuation in the GaAs-GaP solid solution. In n-type GaAs_1−xP_x, the excitons bound at the donor centers $\left({\text{D}}_0^{\text{X}}\right)$ are located at a lower energy (8~13 meV) than those at the ${\text{M}}_0^{\text{X}}$ (Fig. 1, top trace). Inelastic tunneling to the short-lived ${\text{D}}_0^{\text{X}}$ centers is the dominant quenching process for the localized excitons Since the probability of the tunneling is related to the spatial extent of the wavefunction, the exciton wavefunction can be studied through the tunneling processes. Sharp phonon structures appear as the excitation energy is in resonance with the ${\text{M}}_0^{\text{X}}$ band excitons (Fig. 1, λ_L⩾5920Å). The most prominent feature, labelled LA^X, is the LA phonon sideband of the localized excitons at the laser energy. It's narrow linewidth derives from a small energy portion of the localized exciton population which is selectively and resonantly excited by the narrow-width laser. A PL peak M' (Fig. 1, λ_L = 5924Å) occurs at ~3 meV below the laser energy. This "Raman-like" peak persists even at excitation energy well below the ${\text{M}}_0^{\text{X}}$ band (λ_L = 5963Å). The M' band results from excitons created at the laser energy, tunneling to more deeply localized states. The fact that it has a peak rather than a portion of the ${\text{M}}_0^{\text{X}}$ lineshape indicates that the effect of tunneling processes has a dominant role in the exciton luminescence lineshape. Localized exciton at higher energy has a lower fluorescence quantum efficiency due to its more spatially extended wavefunction. Rapid variation of the fluorescence lifetime across the ${\text{M}}_0^{\text{X}}$ band lineshape has also been observed.² The ratio of M' peak intensity to that of the LA^X increases as the laser energy is tuned below the ${\text{D}}_0^{\text{X}}$ peak. This increase is consistant with our model that ${\text{D}}_0^{\text{X}}$ center is the energy sink for the localized exciton.

© 1984 Optical Society of America