Ionizing Radiation Effects in N-Channel (Hg,Cd) Te MISFETs with Anodic Sulfide Passivation

The effect of ionizing radiation, up to a dose of 1.6x105 rad(ZnS)**, on n-channel (Hg,Cd)Te MISFETs, fabricated using anodic sulfide/ZnS insulators, has been investigated. Devices were irradiated under DC bias at 78K. Radiation induced threshold voltage shifts, degraded transconductance, and decreased subthreshold current-gate voltage slopes were observed. For all but the most negative biases during irradiations threshold voltage shifts (a maximum of -6.0 V at 1.6×105 rad(ZnS)) are associated with net hole trapping, with evidence for trapping near the interface for zero applied field during irradiation. Evidence of electron trapping was observed for large negative biases during irradiation. The radiation induced degradation in transconductance is attributed to surface mobility reduction (30% after 1.6×105 rad(ZnS)) associated with scattering from interface charge. The decreassd subthreshold slope (82 mV/decade at 50K after 1.0×105 rad(ZnS)) is attributed to modification of the pre-irradiation gate voltage-surface potential relationship by radiation induced interface traps.