Electron-beam-deposited CdTe layers for passivating Hg1-xCdxTe surfaces

A CdTe film was deposited by electron-beam evaporation on a bulk Hg1-xCdxTe substrate with a composition ratio of x = 0.22 or x = 0.30. The insulating property of the CdTe film was sufficiently good to make MIS (metal-insulator-semiconductor) structures using a CdTe single layer, or a ZnS/CdTe double,layer, as an insulator. Although an almost flatband condition was achieved (Q(f) = 4.5 x 10(10)/cm(2)), Delta V-FB was as large as 1 similar to 2 V, showing a relatively large insulator trapped-charge density. To obtain a fresh HgCdTe surface, in-situ ultraviolet pretreatment in a hydrogen ambient was carried out prior to the deposition of the CdTe. As a result, Delta V-FB was reduced to 0.5 similar to 1.3 V while Q(f) was somewhat increased to 1.5 x 10(11)/cm(2). We fabricated a photovoltaic detector using the CdTe deposition for surface passivation. The HgCdTe photodiode showed good current-voltage characteristics, demonstrating that e-beam-evaporated CdTe films are acceptable for fabricating HgCdTe diodes.