Composition and growth mechanism of anodic oxide on Hg(1−x)CdxTe

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Abstract
The composition of HgCdTe oxides obtained by anodization in a standard KOH/ethylene glycol solution has been determined by Rutherford backscattering spectroscopy for the first time. This technique is advantageous because it is not as surface sensitive as Auger or x-ray photoemission spectroscopy and it provides a nondestructive depth profile of the oxide which can be quantitatively modeled without relying on standards for comparison, as is necessary when using the electron microprobe. The measured composition (61% O, 23% Te, 11.8% Hg, 4.2% Cd for material with x=0.202) is within 0.4% of a stoichiometric mixture of 51.3% HgTeO3, 18.3% CdTeO3, and 30.4% TeO2. While the Hg content in the oxide relative to Te is reduced from the bulk value, it is substantially larger than what is normally reported by other techniques, which found much higher levels of Cd. This composition is consistent with oxide growth occurring primarily by oxygen ions moving into the substrate by a hopping mechanism, while metal ions simultaneously are hopping toward the oxide–solution interface where they can be dissolved into solution. This is the growth mechanism determined by comparing depth profiles after sequential growths in solutions containing KOH and H2O2, the latter solution producing a significant Hg and Cd depletion which can be easily observed by secondary ion mass spectroscopy and Auger electron spectroscopy.

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