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

Rotation anisotropy by second harmonic generation (SHG) is carried out on e pitaxial Hg1-xCdxTe (MCT) and oxide- and sulphide-covered MCT surfaces and shows the fourfold symmetry pattern expected from the {100} surface (C-4 nu 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 d egrees toward the [110] direction. The increase in the SH intensity observe d for the oxide-covered MCT surface is associated with charge accumulation at the MCT/oxide interface since the oxide is centrosymmetric and cannot ge nerate 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 l ength (-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 stage s and absorbs the SH radiation at 532 nm. The rotational anisotropy of the sulphide-covered MCT surface confirms that the CdS layer formed maintains t he cubic closed pack symmetry of the underlying MCT.