Interface properties of various passivations of HgCdTe

Various surface passivations of p-type Hg_1-xCd_xTe were studied to understand their interface properties and their potential for device technology. Anodic oxide forms an inverted layer near the interface. This n-type skin layer exhibits extremely good n-type properties, which equal and even surpass bulk properties. The high electron mobility may be explained by quantization of the electron levels in the space-charge region and the formation of a two-dimensional electron gas near the interface. Thick (approximately 500 angstrom) anodic sulfide generates a similar inversion layer. The charge density is proportional to the sulfide thickness. Carefully prepared thin (approximately 100 angstrom) anodic sulfide films as well as ZnS coating on freshly etched surfaces form nearly flatband conditions that are suitable for n⁺ on p diode technology. The surface recombination velocity, determined for these two passivations using the photoelectromagnetic effect, is shown to be similar at low temperatures, increasing with decreasing temperatures. The dominant trapping mechanism at the surface is similar to that in the bulk and is probably mostly due to vacancies.