The effect of ammonium sulfide treatment on interfacial properties in 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 uses surface passivant for HgCdTe. The effects of sulfidation on the HgCdTe surface and interfacial characteristics of metal/ZnS/HgCdTe structures are studied. The ZnS layer was deposited by thermal evaporation after sulfidation of HgCdTe substrates. The interfacial properties of the metal insulator semiconductor (MIS) structures were determined by capacitance-voltage (C-V) measurements. A comparison of an untreated and a sulfide treated MIS capacitor showed that the fixed charge density and slow state density were 2 and 7 times lower in the sulfide treated specimens 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.