Transfer of excitons bound to nitrogen in GaAs_1-xP_x:N

The time-resolved luminescence of excitons bound to isolated N traps in GaAs1-xPx (x>0.95) has been investigated under low-power resonant picosecond laser excitation. The authors observe a dynamic energy shift of the NX bound exciton luminescence (typically 5 meV for x=0.96) during the first few nanoseconds after the excitation pulse. This result shows that spectral and spatial diffusion of bound excitons occurs within the NX band just after the excitation pulse. The previously reported splitting between the luminescence and absorption of the bound exciton is explained by this transfer. Under 10 kW nitrogen laser excitation, one observes the filling of the NX band, which delays the exciton migration. With this high excitation, a new broad line due to collective exciton effects at the N traps is also observed in time-resolved spectra.