The Effect of Gamma Irradiation on the Low Temperature Properties of Amphoterically Si‐Doped GaAs LED's

Abstract

The effects of gamma irradiation on the light intensity, total current, spectral characteristics, and radiative decay time as a function of applied voltage at 76~ have been studied in amphoterically Si-doped GaAs lightemitting diodes (LED's). At low voltages, both the total current, I, and radiative current are due to space charge recombination with the result that, at constant voltage, I increases with gamma dose, r while the light intensity, L, remains constant. At higher voltages, where the radiative current is due to recombination in the neutral p-region, L decreases sharply with r at constant voltage. This rapid decrease is due, in part, to the presence of space-charge limited current (SCLC) flow which also leads to a decrease in I with r at constant high voltage. Spectral measurements show that the emission peak energy is proportional to junction voltage at low currents suggesting radiative tunneling of carriers in deep tail states. In accordance with the "wavy band" model t'or these diodes, tail states are also responsible for the observed inverse dependence of radiative decay time on diode current and emitted photon energy. The long lifetimes in the localized deep tail states lead to a radiation damage effect contrary to that observed for diffusion length-associated lifetimes; that is, the longest lifetimes are least affected by gamma irradiation.