CdTe/ZnS composite passivation layers were grown with different processes, and the corresponding LW HgCdTe gate-controlled diodes were fabricated. The I-V measurement and analysis were carried out under different conditions for these devices. The results show that the polarity of the fixed interface charge is positive and interface charge density is high for the device prepared by the standard process. The large leakage current in the surface channel is formed under high reverse bias voltage, which has an important effect on the performance of the device. The fixed interface charge density is effectively reduced by improvement of the growth process of the passivation films, which changes the HgCdTe surface from weak inversion gradually to the flat band condition. The surface effect is effectively suppressed, thus the reverse characteristics of the device can be improved significantly. In addition, the number of interface traps has been greatly reduced for the device prepared by the optimized process condition, and the stability of the device is enhanced. There is no obvious change in R0A of the device with the gate voltage.