Neutron Damage in Epitaxial GaAs Laser Diodes

Abstract

The effects of neutron irradiation on the radiative, nonradiative, and threshold currents in epitaxial GaAs laser diodes have been studied at room temperature and 76°K. At 300°K for currents below the threshold, most of the current flows by recombination in the space-charge layer, but the radiative current is due to minority carriers thermally injected into the p-type region. Neutron irradiation does not significantly affect these current flow mechanisms. However, it does lead to a reduction in light intensity and an increase in total current through the introduction of nonradiative recombination centers which reduce the lifetime in both the space-charge and neutral regions. Neutron irradiation has less of an effect on the diode properties at 76°K. The radiative current, which is apparently due to tunneling, is rather insensitive to irradiation when the voltage is held constant. However, at constant current the light intensity decreases with neutron fluence although not as rapidly as in the constant current case at 300°K. Similar to the results at 300°K, the total current increases with irradiation; the additive current being due to space-charge recombination and nonradiative tunneling. The laser threshold current increases with neutron irradiation by a multiplication factor which is approximately independent of temperature. The changes in JT can be accounted for by assuming that the neutron-induced nonradiative recombination centers lead to a decrease in the internal stimulated quantum efficiency. Very little annealing of the light degradation was observed between 19° and 550°K. No neutron-induced time delay in laser turn on was detected.