Photoluminescence study of excitons localized in indirect-gapGaAs1−xPx

A novel structure ($M_0^X$) in the photoluminescence spectra from $n$-type indirect-gap $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$ alloys has been studied in detail. It has an asymmetric line shape and prominent $X$-point phonon sidebands. Its binding energy relative to the free-exciton band edge ($E_{\mathrm{gx}}^X$) is very shallow. The characteristic lifetime of fluorescence decay has been found to vary rapidly over the $M_0^X$ band linewidth. It is proposed that the $M_0^X$ band is due to exciton bound by potential wells resulting from the alloy compositional fluctuation. The narrowing of the $M_0^X$ band's linewidth at rising temperatures and the temperature quenching of fluorescence with the excited state can be accounted for by the strong energy dependence of the effective range of the localized exciton wave function. The decrease of the $M_0^X$ quantum efficiency with increasing laser power is attributed to Auger decay of biexcitons.