Radiative recombination mechanisms in GaAsP diodes with and without nitrogen doping

Abstract

The electroluminescent properties of GaAs1−xPx light-emitting diodes with and without nitrogen doping have been studied at temperatures from 77 to 300 °K. The radiative transitions in the indirect band-gap region have been identified by a comparison of the emission spectra with those obtained in GaP. At 77 °K nitrogen-free GaAsP recombination consists of three peaks, shallow donor-acceptor pair transitions, free-exciton transitions (which are not observed in pure GaP), and LA phonon-assisted free-exciton transitions. As the temperature is increased, the free excitons and/or free electron-hole transitions become dominant. The indirect energy band gap has been found to exhibit appreciable curvature. The alloy composition at which the direct-indirect energy band-gap transition occurs has been found to be xc=0.46 at 77 °K and 0.49 at 300 °K. In nitrogen-doped GaAsP the 77 °K emission is dominated by transitions associated with nitrogen. For alloy compositions near GaP (x ≥ 0.9) a series of distinct peaks are observed, corresponding to the sharp-line nitrogen spectrum commonly observed in GaP. For x<0.80 the distinct peaks converge into a single broad band. Optical-absorption measurements indicate that both the depth and width of the nitrogen absorption band increase with increasing As concentration. The electroluminescent recombination for x < 0.80 has been found to occur primarily in a NN pair band, the high-energy onset of the EL band corresponding roughly to the center of the absorption band.