Neutron damage in GaP : Zn,O light-emitting diodes

Electrical and optical measurements have been carried out at 300 K to ascertain the effects of neutron irradiation on the properties of red-emitting GaP : Zn,O light-emitting diodes. Capacitance measurements at 300 K indicate that majority-carrier removal is insignificant below a neutron fluence Phi of 1015 n/cm2. Above this value, a removal rate of 6.5 cm-1 is found. Current-voltage data show that the total current increases with Phi at constant voltage and that the neutron-added current is due to space-charge recombination. The rate of increase in current with Phi leads to a lifetime--damage-constant product tauK of (3.0 +- 0.9) x 10-14 cm2. A similar analysis of the degradation of the light output, which is due to a diffusion current at 300 K, results in tauK= (2.4 +- 0.4) x 10-14 cm2. This analysis also reveals that near the junction in the p region the concentration of Zn-O pairs is linearly graded as is the Zn profile according to the capacitance data. Curves of efficiency versus current measured at 300 K possess maxima which decrease in magnitude and shift to higher current densities with increasing Phi. These results are indicative of saturation of the Zn-O centers at high injection levels. The rate of decrease of the maxima with Phi leads to a tauK value of (2.0 +- 0.6) x 10-14 cm2 and suggests that the Zn-O profile is also linearly graded a few diffusion lengths from the junction. The agreement between the various tauK values tends to support the damage model employed in which neutron irradiation results in the introduction of nonradiative recombination centers in both the depletion and neutral regions