Neutron Irradiation Effects on Diffused GaAs Laser Diodes

The effects of fast neutron damage on diffused GaAs laser diodes have been studied by observing the pre- and post-irradiation current-voltage characteristics and electroluminescence (EL) spectra at several temperatures between 75°K and 300°K. The pre-irradiation diode current at high temperature is dominated by nonradiative space-charge region recombination. The principal emission band at 300°K results from band-to-acceptor recombination in the p-region. A secondary band at 1.28 eV occurs via donor-acceptor pair recombination in the depletion region. At low temperature the dominant diode current flow is by nonradiative tunneling while the principal emission band contains radiative tunneling and band-filling components. Neutron irradiation increases the constant-voltage diode current. The additional current is due to space-charge region recombination (SC) at high temperatures and both SC and tunneling at low temperatures. The room-temperature damage constant is somewhat larger than that found in epitaxial GaAs laser diodes and in silicon p+n diodes. The constant-voltage principal emission band intensity decreases with fluence at a rate such that the resultant damage constant is about half that of the SC current damage constant. Irradiation to a fluence of 1.8 × 1015 n/cm2 (> 10 keV) has no effect on the constant-voltage secondary emission band intensity.