|Abstract:The MW HgCdTe avalanche photodiodes (HgCdTe APDs) were prepared by different processes. The pn junction characteristic and the relation between gain and bias voltage for HgCdTe APDs were characterized by different methods. The gain-bias curves of APDs were fitted based on the Beck model and Shockley,s analytical expression. The results show that the widths of the saturated depletion region for APDs fabricated by different processes are 1.2μm and 2.5μm respectively. The wide depletion region effectively suppresses the tunneling current at high reverse bias, and Shockley,s analytical expression has been found to give an excellent fit to the gain–bias curves of HgCdTe APDs, and fitting parameters are similar to the results of Rothman at Sofradir.