Radiative recombination mechanisms in GaAsP diodes with and without nitrogen doping

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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 xx < 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.