Neutron Damage in GaAs Laser Diodes: At and above Laser Threshold

The effects of fast neutron damage on GaAs laser diodes have been examined with the following results: (1) Infrared photomicrographs of laser output for diodes operating above threshold at 300 K reveal that neutron irradiation does not have a significant effect on the near-field spatial distribution. (2) Neutron irradiation of a group of laser diodes of different cavity lengths demonstrates that the damage-induced increase in threshold current at 300 K is due primarily to a decrease in gain factor. The rate of decrease of the gain factor with neutron fluence agrees with that predicted by a previously determined damage constant. (3) Preliminary measurements of total light output as a function of diode current at 300 K and 76 K show that the lasers are much less sensitive to neutron damage at currents significantly above threshold. In fact, for some diodes the light output at 76 K increases at a given current with neutron irradiation for fluences as high as 3 × 1014 n/cm2.