Ammonium sulfide treatment of HgCdTe substrate and its effects on electrical properties of ZnS/HgCdTe heterostructure

Abstract

The semiconductor–passivating layer interface, as well as the dielectric properties of the passivants, plays an important role in HgCdTe based photodiodes. ZnS is a commonly used surface passivant for HgCdTe. This study examined the effects of sulfidation on the HgCdTe surface and interfacial characteristics of metal/ZnS/HgCdTe structures. The ZnS layer was deposited by thermal evaporation after sulfidation. The interfacial properties of the metal insulator semiconductor (MIS) structures were determined. A comparison of an untreated capacitor and a sulfide treated MIS capacitor showed that the fixed charge density (untreated 6.37×10 11, treated 3.2×10 11 cm −2) and slow state density (untreated 5.5×10 11, treated 7.5×10 10 cm −2) were 2 and 7 times lower in the treated than in the untreated specimens. Sulfidation results in a decrease in the concentration of contaminants originating from the native oxide-covered HgCdTe substrates. This reduction may be due to the formation of S–S or II–S bonds at the surface layer. These bonds might act as barriers against native oxide formation when (NH 4) 2S x-treated HgCdTe substrates are exposed to air.