Time-resolved photoluminescence study of radiative transition processes in GaP1- x N x alloys

Time-resolved photoluminescence (PL) measurements reveal that the radiative transition and carrier relaxation processes in GaP_{1- x} N _x alloys with high N concentrations are significantly different from those with low concentrations where NN _i lines are clearly observed. The PL decay curve shows two distinct exponential processes for high concentrations while it is represented by a single exponential for low concentrations. The slow decay in GaP_{1- x} N _x alloys with high N concentrations indicates both the long radiative lifetime caused by the weak localization of excitons and the slow relaxation due to the scattered spatial distribution of the states. This is consistent with the fact that the PL occurs at the tails of density of states, which is found from the comparison between absorption and PL spectra.