Reconstruction and stoichiometry of CdTe(001) surfaces. A grazing incidence X-ray diffraction and reflection high energy electron diffraction study

We present X-ray diffraction measurements on the CdTe(001) surface. In-plane and out-of-plane scattering were used to solve the structure of the c(2 X 2) surface. The basic structural unit consists in two Cd atoms bounded to Te in an almost flat ''bridge model'' giving a coverage of 0.5 ML Cd. This arrangement is followed by a strong relaxation of the underlying substrate down to the sixth atomic layer. This model is in full agreement with the first principles calculations for the ZnSe c(2 X 2) structure. A strong anisotropy of the reconstructed domain dimensions was observed, for the surfaces formed above 280 degrees C. For the low temperature (2 X 1) Te surface, a new method has been applied to determine the surface stoichiometry. This method is based on the variation of the specular beam intensity in reflection high energy electron diffraction (RHEED) during the homoepitaxial growth, combined with the results obtained for the relaxation in highly strained CdTe/ZnTe structures grown by atomic layer epitaxy. The coverage of the (2 X 1) Te surface was estimated to be 1.5 ML.