Vacuum Baking Effects on the I-V Characteristics of LWIR HgCdTe Photodiodes with Different Passivation

摘要

HgCdTe infrared detector is designed to operate at cryogenic temperatures, so vacuum baking is a required process forout-gassing in packaging of devices. As HgCdTe material , as well as ZnS passivation layer is sensitive to heat induced changes, this process may be problematical for HgCdTe devices even at relatively low temperatures. We try to solve theproblems of heat instability by the fabrication of CdTe/ZnS double passivation layers. The effect of vacuum baking isinvestigated through current-voltage (I-V) characteristics. We have compared the effects on devices with differentpassivation layers. We have also compared the photodiodes fabricated on MBE grown HgCdTe on GaAs substrates andLPE grown HgCdTe on CdZnTe. The devices were passivated with electron beam evaporated CdTe and ZnS and the p-njunction was formed by ion-implantation. Through the analysis of I-V characteristics, we found that the devicespassivated with ZnS cannot afford vacuum baking even at 70C°, while the CdTe/ZnS- passivated devices can afford upto 110C° temperature and the performance improved. After only 4 hours baking, the dynamic resistance of ZnSpassivation devices began to decrease and 10 hours later the zero-bias dynamic resistance (Ro) decreased nearly 3 times.Further baking of 110C° sees the maximum dynamic resistance of CdTe/ZnS passivation devices increase 2 to 4 times.An insight into the mechanisms and parameters that are affected by vacuum baking is also gained by resistance-voltage(R-V) curve fitting. The results also indicated the baking effects on LPE grown HgCdTe devices are almost same toMBE grown HgCdTe devices.