Experimental and theoretical results are presented for current-voltage and dynamic resistance-voltage characteristics of Hg1-xCdxTe ion-implanted p-n junction photodiodes with x approximately equals 0.22. By measuring the temperature dependence of the dc characteristics in the temperature range 25-140K, the dark current mechanism are studied. At high temperature and in low reverse bias region, the diffusion current dominates. On the other hand, at medium temperature and medium reverse bias, trap-assisted tunneling plays an important role. At low temperature and in the medium reverse bias region, band-to-band tunneling is the key leakage current source.However, when the temperature is further lowed down to 25K and the applied reverse bias is very small, the band-to-band tunneling current will be ruled out and the trap-assisted tunneling mechanism dominates again. We have measured 1/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 value and the maximum signal-to-noise ratio are about 3.51 X 1010 cm Hz1/2/W and 5096 respectively.