Surface second harmonic generation in the characterization of anodic sulphide and oxide films on Hg1-xCdxTe (MCT)

Berlouis, L.E.A. and Wark, A.W. and Cruickshank, F.R. and Pugh, David and Brevet, Pierre-Francois (1999) Surface second harmonic generation in the characterization of anodic sulphide and oxide films on Hg1-xCdxTe (MCT). Journal of Electronic Materials, 28 (6). pp. 830-837. ISSN 0361-5235

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Abstract

Rotation anisotropy by second harmonic generation (SHG) is carried out on epitaxial Hg1−xCdxTe (MCT) and oxide- and sulphide-covered MCT surfaces and shows the fourfold symmetry pattern expected from the {100} surface (C4v symmetry). The uneven nature of the four peaks confirm the vicinal surface obtained from the growth of the MCT on GaAs {100} substrate orientated 4° toward the 〈110〉 direction. The increase in the SH intensity observed for the oxide-covered MCT surface is associated with charge accumulation at the MCT/oxide interface since the oxide is centrosymmetric and cannot generate SH. The CdS layer on the other hand is strongly nonlinear active and generation here comes from a composite of one noncentrosymmetric layer on top of another. This leads to interactions in the observed SH arising from the coupling depths (∼40 nm) at the two interfaces and from the coherence length (∼1200 nm) in the CdS layer. The in-situ SHG measurements during the growth of the anodic oxide and sulphide layers would suggest that a species, most likely HgTe is embedded in the anodic layer during the initial stages and absorbs the SH radiation at 532 nm. The rotational anisotropy of the sulphide-covered MCT surface confirms that the CdS layer formed maintains the cubic closed pack symmetry of the underlying MCT.