Optical and field effect studies of the Hg0.7Cd0.3 Te–anodic oxide interface

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Abstract
This paper reports the effects of visible light and applied electric field on the properties of the HgCdTe–anodic oxide interface. The surfaces of anodized n‐type crystals are accumulated with a fixed positive charge in the oxide on the order of 5×1011 cm−2. However, illumination with photons of energy ?2.2 eV can neutralize and even invert these surfaces. The original surface charge is restored by placing the sample in the dark for periods of minutes at room temperature and weeks at 77 K. Based on our measurement of the oxide energy gap of 3.4 eV, the photo‐induced surfacecharging is attributed to internal photoemission of electrons from the HgCdTe valence band to the oxide conduction band. These photoemitted electrons fall into deep traps in the oxide and neutralize the fixed positive charge. When stored in the dark, these trapped electrons are thermally excited from the traps and recombined in the semiconductor.Charge exchange between the oxide traps and semiconductor can also be promoted by applying an electric field across the interface. Charge exchange occurs via tunneling, and the rate of charge exchange increases strongly with temperature, indicating that the trapped charge is distributed in energy. This effect saturates as the excess charge in the oxide neutralizes the applied field. Thus, under constant applied field, the original band bending in the semiconductor is eventually restored. From the temperature and time dependences of the trapping, the oxide traps are likely distributed both in energy and in distance from the semiconductor.

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