Laser induced effects in HgCdTe photovoltaic devices

In this paper we report on induced persistent dark currents in HgCdTe photodiodes induced with lasers, and relationships of these effects with those observed with γ rays and high‐energy electron irradiations. Front side laser illumination with relatively small photon flux induces changes in the dark currents with thermal recovery characteristics similar to those observed from irradiation experiments with Co⁶⁰ gammas and high‐energy electrons. The induced currents produced by these alternative sources are mostly of tunneling origin. The degree of susceptibility to irradiation and illumination observed on devices of different structures is found to be similar, i.e., devices with relatively hard characteristics when exposed to irradiation with γ rays or high‐energy electrons also are observed to be hard to laser illumination. Our results indicate that these metastable effects produced by lasers, γ rays, and high‐energy electrons are of a common origin. The laser experiments suggest that these effects are associated mostly with changes in the electronic properties in the vicinity of the semiconductor junction at the insulator interface. The magnitude of the change in the dark current decreases with increasing wavelength of light and band‐gap light produces no notable changes. This observation suggests a threshold energy for producing the effects and suggests that the physical processes are excitation of carriers from the semiconductor into the insulator/interface region. Junction parameters and the material features of the insulator/semiconductor interface are shown to be important factors in determining the susceptibility of devices to irradiation and illumination.