Electrical properties of the SiO2:HgCdTe interface

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Abstract
By determining the dependence of flatband bias on insulator thicknesses in MIS devices made with PHOTOX SiO2 on n‐type Hg0.7Cd0.3Te, we have for the first time determined the amount of interface charge and the effective work function of the semiconductor surface. Flatband bias was determined from the surface potential as obtained by Berglund integration of quasistatic capacitance measurements at 77 K. Insulator thickness was varied from 500 to 4000 Å. The amount of fixed charge was seen to vary between −0.3×109 cm−2 and +8×1010 cm−2 depending on the type of deposition sequence used. It was also seen that H2O could be absorbed into the layer and removed by vaccum baking at temperatures of 60–100 °C and resulted in a change of interface fixed charge of up to 8×1010 cm−2. This is in agreement with the range of charge variation seen above. The presence of large amounts of H2O also was seen to introduce surface states at 0.06 and 0.14 eV above the valence band edge (Eg=0.24 eV at 77 K). The effective work function difference between the Ti/ Au bilayer gate and the HgCdTe surface was determined to be +0.03 V ±0.05 V.

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