At present, infrared photodetectors are being increasingly used in space systems, where they are exposed to the space radiation environment. Consequently, the radiation-hardness-related problem in HgCdTe photodetectors has become a critical issue.
In this study, the gamma radiation effects on ZnS- and CdTe-passivated mid-wavelength infrared (MWIR) HgCdTe photodiodes were investigated. Although ZnS has an excellent insulating property, its radiation-tolerant property was revealed very poor in comparison with CdTe. After 1 Mrad of gamma irradiation, the resistance-area product at zero bias (R0A) value of the ZnS-passivated photodiode was drastically reduced by roughly 5 orders from ~107 Ω cm2 to 102 Ω cm2, whereas the CdTe-passivated photodiode showed no degradation in R0A values.
Surface treatment is one of the key issues for fabricating long-wavelength infrared (LWIR) detectors having good performance. In this paper, a novel surface treatment using hydrazine has been proposed for HgCdTe and its validity has been confirmed with ellipsometry and C-V analysis. The fixed charge density and trap oxide charge density of hydrazine-treated sample have shown so small value of 1.29×109 cm-2 and 4.35×1010 cm-2, respectively, comparing with those obtained with the conventional Br-MeOH-treated sample. In addition, the hydrazine-treated sample has shown high frequency characteristic in the C-V curve, which means the large effective minority carrier lifetime on the surface. By applying the new surface treatment using hydrazine to vacancy-doped wafers, LWIR photodiodes have been successfully fabricated. Current-voltage (I-V) characteristics of the hydrazine-treated Hg0.77Cd0.23Te diodes were also measured. Average R0A products of these diodes with the junction area of 30x30 μm2 were about 2.54 Ωcm2, which satisfy 95% BLIP (background limited infrared photodetector) condition for LWIR photodiodes.