Dark currents in HgCdTe photodiodes passivated with ZnS/CdS

Experimental and theoretical results are presented for current-voltage and dynamic resistance-voltage characteristics of Hg_1-xCd_xTe ion-implanted p-n junction photodiodes with x ≈ 0.22 passivated with ZnS/CdS layers. By measuring the temperature dependence of the dc characteristics in the temperature range 25-140 K, the dark current mechanisms are studied and the validity of the modeling is confirmed. It was found that the dark currents can be represented with three current components over a broad range of voltage and temperature. At high temperature (>90 K) and in low reverse bias region, the diffusion current dominates. On the other hand, at medium temperature (40-80 K) and medium reverse bias (< -0.15 V), trap-assisted tunneling plays an important role. At low temperature (<40 K) and in the medium reverse bias region (< -0.15 V), band-to-band tunneling is the key leakage current source. However, when the temperature is further lowered to 25 K and the applied reverse bias is very small (-0.15 to 0 V), the band-to-band tunneling current will be ruled out and the trap-assisted tunneling mechanism dominates again.