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

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 6.37×1011, treated 3.2×1011 cm−2) and slow state density (untreated 5.5×1011, treated 7.5×1010 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 (NH4)2Sx-treated HgCdTe substrates are exposed to air.