Band offsets and interfacial properties of cubic CdS grown by molecular-beam epitaxy on CdTe(110)

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 ${\mathrm{\Gamma }}_8$ valence-band maximum is lower by Δ${\mathrm{\varepsilon }}_{\mathrm{VB}}$=0.65 eV. Taking the known band gap of cubic CdS (2.42 eV) lets us estimate the ${\mathrm{\Gamma }}_6$ conduction-band minimum of CdS to be above that of CdTe by Δ${\mathrm{\varepsilon }}_{\mathrm{CB}}$=0.21 eV. Our theoretical estimates based on dielectric midgap tight-binding calculations, including the hydrostatic contribution of the ∼11% tensile lattice strain in the cubic CdS epilayer, predict a much larger valence-band offset of Δ${\mathrm{\varepsilon }}_{\mathrm{VB}}$=1.19 eV.