Interface properties and surface leakage of HcCdTe photodiodes

A program was undertaken to determine the origin of surface leakage associated with Hg sub 1-x Cd sub x TE photodiodes and to seek improved surface passivation techniques. To attain this goal, emphasis was placed on surface spectroscopic analyses and metal-insulator-semiconductor (MIS) characteristics of candidate passivants. During the initial four months of the program, the insulating and interfacial properties of anodic oxides and ZnS on Hg0.8Cd0.2Te were investigated. X-ray photoelectron spectroscopy (XPS) techniques were developed for determining depth profiles of compositional variations in the semiconductor with a minimum materials damage. Using these techniques, we found that (a) the composition of a 1200 angstrom anodic film is 68% Te02, 27% CdO, and 6% HgO, and (b) the cations, especially the Hg ions in the semiconductor, are significantly depleted near the interface. The capacitance-voltage curves from MIS measurements of the same specimen exhibited a large hysteresis and a characteristic indicative of a high density of surface states. The consequence of these chemical and electrical properties to diode passivation is discussed.