Abstract
We report on the molecular-beam-epitaxy growth of CdS films on CdTe(110), studied with reflection high-energy electron diffraction (RHEED) and angle-resolved photoemission spectroscopy. The exponential attenuation of the Te 4d core-level emission as a function of the CdS film thickness and the persistency of the substratelike RHEED pattern demonstrate that CdS films grow epitaxially in the zinc-blende structure rather than the thermodynamically more favorable hexagonal crystal structure. Core-level intensity and line-shape analysis show that the interface is atomically abrupt and nonreactive. From valence-band photoemission spectra, we find that, compared with CdTe, the CdS ${\mathrm{\ensuremath{\Gamma}}}_{8}$ valence-band maximum is lower by \ensuremath{\Delta}${\mathrm{\ensuremath{\varepsilon}}}_{\mathrm{VB}}$=0.65 eV. Taking the known band gap of cubic CdS (2.42 eV) lets us estimate the ${\mathrm{\ensuremath{\Gamma}}}_{6}$ conduction-band minimum of CdS to be above that of CdTe by \ensuremath{\Delta}${\mathrm{\ensuremath{\varepsilon}}}_{\mathrm{CB}}$=0.21 eV. Our theoretical estimates based on dielectric midgap tight-binding calculations, including the hydrostatic contribution of the \ensuremath{\sim}11% tensile lattice strain in the cubic CdS epilayer, predict a much larger valence-band offset of \ensuremath{\Delta}${\mathrm{\ensuremath{\varepsilon}}}_{\mathrm{VB}}$=1.19 eV.
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