Radiation Damage Induced Time Delay in GaAs Lasers

Fast-neutron irradiation induced time delays in the turn-on of the optical output pulse of diffused GaAs laser diodes have been observed. The results are explained using a double-acceptor model that predicts the delay\´s functional dependence on fluence and that also accounts qualitatively for the observed temperature dependence of the delay. Little neutron damage induced change occurs at LN2 temperature, where the delay is thought to be a result of the time required to establish the population inversion, the double-acceptor traps being inactive. At high temperature the increase in delay with fluence appears to be caused by introducing more traps at a rate proportional to the number already existing. A "pivot" operating point can be found at which the diode time delay is almost unaffected by damage to > 1014 n/cm2 (> 10 keV).