Dark current mechanisms in HgCdTe photodiodes

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. By measuring the temperature dependence of the dc characteristics in the temperature range 25-140 K, the dark current mechanisms are studied 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 volt), trap-assisted tunneling plays an important role. At low temperature (<40 K) and in the medium reverse bias region (<-0.15 volt), band-to-band tunneling is the key leakage current source. However, when the temperature is further lowed down to 25 K and the applied reverse bias is very small (-0.15∼0 volt), the band-to-band tunneling current will be ruled out and the trap-assisted tunneling mechanism dominates again. We have measured l/f noise in HgCdTe photodiode as a function of temperature, diode bias, dark current. The dependence of 1/f noise on dark current was measured over a wide temperature range on devices. The temperature dependence of the 1/f noise was found to be the same as the temperature dependence of the surface generation and leakage currents. We obtained the maximum specific detectivity (D*) value and the maximum signal-to-noise ratio are about 3.51 × 10¹⁰ cm·Hz^1/2/W and 5096, respectively.