A comparison of gamma-induced degradation and forward bias-induced degradation in GaP:Zn,0 LEDs

Both the effects of gamma irradiation and high-current forward bias on GaP:Zn,0 light emitting diodes (LEDs) have been studied by measuring constant current 76K electroluminescence (EL) spectra below 1000 nm, total light output at room temperature, and capacitance transients using the technique of deep level transient spectroscopy (DLTS). The LEDs were divided into two sets; a control set which was subjected only to forward bias, and a set exposed to gamma irradiation and forward bias. The results indicate that gamma-induced light output degradation occurs through a different mechanism than forward bias-induced degradation of the control LEDs. Gamma irradiation, which has no effect on the Zn-O concentration, degrades the light output through the introduction of competing non-radiative recombination centers which reduce the minority carrier lifetime. In contrast, forward bias-induced light output degradation is primarily due to a reduction in Zn-O concentration through the apparent recombination-enhanced interaction of Zn-O centers with impurities rather than defects. This work was supported in part by the Air Force Weapons Laboratory (AFWL) Kirtland AFB, Albuquerque, NM under P. O. 77-027, and in part by the U. S. Department of Energy (DOE) under contract number AT(29-1)789.