Modeling the Radiation Effects in MERCURY(1-X) Cadmium(x) Telluride Diodes.

The effects of radiation induced surface traps and bulk damage in long wavelength infrared Hg _{1-x}Cd_{x}Te (MCT) pn junction diodes are modeled in a numerical device simulator. The modified simulation program was used to determine the role of interface traps and bulk damage in passivated MCT devices. A band-to-band model is developed and included into the simulation program. The band-to-band tunneling model accounts for some, but not all, of the increased currents observed in irradiated MCT pn junction diodes. The trap-assisted tunneling model is included in the simulation program and the simulation program is capable of producing a current-voltage relationship which matches those from measurements using a combination of parameter values. The parameter values are analyzed using physical arguments and the dose dependence of the currents at reverse bias. The model provides the most accurate results when the model uses the local bulk conditions to establish whether trap -assisted tunneling is possible. This work provides evidence that ionizing radiation affects MCT pn junction devices by damaging at the passivation and introduces a high concentration of near-interface bulk trapping sites. The interface trap sites trap holes and bend the surface energy bands to the point of inversion. They increase the band-to-band tunneling contribution to the current. The bulk traps tend to increase trap-assisted tunneling and may hold negative charges for a sufficient time to appear to increase their lifetime.