The characterization of anodic fluoride films on Hg1−xCdxTe and their interfaces

Abstract

A novel anodic fluoridization process for forming native fluoride films on Hg1−xCdxTe is described. As in the case of the anodic oxide, the anodic fluoride grows in two steps: a dissolution–precipitation step is followed by a bulk growth. Anodic fluorides free of oxygen are grown from nonaqueous solutions. The presence of water causes the growth of films containing both fluorine and oxygen, whereas a low hydroxyl ion concentration causes the growth of anodic oxide alone. However, its electrical behavior is different from that of anodic oxide grown from fluoride‐free baths. The results of Auger electron spectroscopy analysis indicate that the anodic fluoride is composed of cadmium fluoride in a matrix of tellurium, cadmium, and mercury. The fluoride is homogeneous and has a relatively abrupt dielectric–semiconductor interfacial transition, free of contaminants. Metal–insulator–semiconductor devices containing a fluoride film and evaporated ZnS have been fabricated and characterized. By choosing an appropriate ratio of fluoride to hydroxyl ions in the anodization bath the band bending at the n‐type Hg1−xCdxTe surface can be adjusted from near flatband conditions to strong accumulation. Anodization from a nonaqueous solution results in a p‐type Hg1−xCdxTe surface that is slightly depleted due to a fixed charge density of ∼5×1010 cm−2. There is only a negligible density of both slow and fast surface states. Low and reproducible surface state densities are achieved by a short dissolution–precipitation step. Such interfaces are stable up to 105 °C.