It has been determined that anodic oxidation of (Hg,Cd)Te occurs via a dissolution-precipitation mechanism followed by a bulk growth process which involves either interstitial transport of metal cations and/or hydroxyl anion transport via successive jumps. The initial film formation can be understood at least partially in terms of electrochemical parameters and, therefore, can be controlled in a rational manner. For example, stirring the anodization solution during dissolution prohibits film formation due to an increase in the rate of diffusion of ionic species away from the anode. MOS structures fabricated incorporating this electroetch in the passivation process show unique properties which provide evidence for a direct correlation between initial oxide formation and the resultant (Hg,Cd)Te surface electronic properties.

We have demonstrated the controlled growth of photochemical native oxide on (Hg, Cd)Te by the UV photodissociation of N2O. The initial growth rate is ∼7Å/min, is insensitive to temperature over the range from 40 to 100 °C, and is dependent on the surface Hg concentration. Encapsulation of the native oxide with photochemical SiO2 results in a degradation of the (Hg, Cd)Te–native oxide interface electrical properties. The presence of photochemical HgO between the native oxide and SiO2 results in superior (Hg, Cd)Te surface electronic properties. However, MOS structures comprising SiO2 on a double layer of HgO on photochemical native oxide undergo an electrical degradation at room temperature, likely owing to reactions between HgO and the native oxide or (Hg, Cd)Te substrate.

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SiO2 deposited photochemically at a substrate temperature of 100 °C has been evaluated as a surface passivant on Hg1−xCdxTe  (x=0.30). It has been determined that the electrical properties of the (Hg, Cd)Te–SiO2 interface are dependent on the pretreatment given the semiconductor surface prior to the insulator deposition. Formation of a thin native oxide on the (Hg, Cd)Te surface during the pretreatment appears to enhance the resultant (Hg, Cd)Te–SiO2 interface properties. A significant spread in the (Hg, Cd)Te–SiO2 interface properties is observed, likely owing to the nature of how this native oxide forms and interactions between the native oxide and the SiH4 in the photochemical reactor. It is shown through neutron activation analysis that the Hg employed as a photochemical sensitizer is incorporated in the SiO2 at a concentration of 1.8 ppm.