Effect of atmosphere on n-Type Hg _1-x Cd _x Te surface after different wet etching treatments: An electrical and structural study

The impact on surface recombination velocity (SRV) and minority carrier lifetime of three wet etchants are examined here. The etchants are 60DI + 10HBr + 1H ₂O ₂ (by volume), 1% bromine-methanol, and 2% bromine-lactic acid. After initial etching, the HgCdTe surfaces were exposed in specific time steps to the atmosphere. At each step in the process, the effect of each etchant and of exposure to atmosphere was determined by photoconductive decay (PCD) measurements as well as by x-ray photoelectron spectroscopy (XPS). The PCD results showed that the 60DI + 10HBr + 1H ₂O ₂ etchant, after exposure to atmosphere, led to a relatively small change in SRV compared to the changes that occurred for the two bromine-based etchants. In addition, XPS measurements showed that there were no neutral tellurium inclusions in the case of 60DI + 10HBr + 1H ₂O ₂ and that TeO ₂ formed strictly out of tellurium bonded to HgCdTe. Moreover, TeO ₂ formed at a much slower rate on surfaces etched with HBr compared with those etched with the bromine-based etchants. A model is proposed in terms of band alignment at HgCdTe-Te ⁰ and HgCdTe-TeO ₂ interfaces to explain the different surface recombination mechanisms that are due to different etchants and to atmospheric exposure.