Electrical and Computer Engineering ETDs

Publication Date



A study has been made on the effects of fast neutron irradiation on time delay occurring in diffused GaAs laser diodes operating at 77° K and 300° K. Measurements were performed at 300° K prior to irradiation and thence after successive exposure to neutron irradiation to a maximum of about 1.2 x 10^14 nvt (>10 KeV). At 77° K, measurements were limited to a pre-irradiation characterization and a characterization after the final irradiation. A double acceptor model is used to account for the observed changes in the delay characteristics as a result of both temperature changes and neutron irradiation. In this model, delays at 300° K are a result of traps that exist at energies near the bottom of the conduction band, which prevent lasing by absorbing photons. Lasing occurs when these traps capture sufficient electrons from the conduction band to become nonabsorbing. It appears that neutron irradiation induces similar traps into the material, the result being an increase in the delay when the diodes are operated at constant current. However, when the diodes are operated at a constant multiple of threshold current, the delay is observed to either increase or decrease, depending on the relative magnitudes of the threshold and driving currents. At small multiples of the threshold current, the delay decreases as a result of irradiation; at higher multiples the effect of irradiation is to increase the delay. Between these two extremes is an operating point where radiation-induced changes in the delay are a minimum. The double-acceptor model successfully predicts the existence of this point, and furthermore, establishes a maximum radiation-induced delay which is the same for all currents and compares favorably with the results. At 77 ° K, the delays in both the unirradiated and irradiated diodes appear to be due to the time necessary to create a population inversion. The implication is that the delay-inducing traps are absent at low temperatures, a result predicted by the double-acceptor model.

Document Type




Degree Name

Electrical Engineering

Level of Degree


Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Harold Dean Southward

Second Committee Member

Roy Arthur Colclaser

Third Committee Member

Wayne Willis Grannemann