Band offsets for mismatched interfaces: The special case of ZnO on CdTe (001)

High-quality planar interfaces between ZnO and CdTe would be useful in optoelectronic applications. Although CdTe is zinc blende with cubic lattice constant a 6.482 angstrom while ZnO is hexagonal wurtzite with a = 3.253 angstrom and c = 5.213 angstrom, (001)-oriented cubic zinc blende ZnO films could be stabilized epitaxially on a CdTe (001) surface in an root 2 x root 2 R45 degrees configuration with a lattice mismatch of < 0.5%. Modeling such a configuration allows density-functional total-energy electronic-structure calculations to be performed on several interface arrangements (varying terminations and in-plane fractional translations) to identify the most likely form of the interface, and to predict valence-band offsets between CdTe and ZnO in each case. Growth of ZnO on Te-terminated CdTe(001) is predicted to produce small or even negative (CdTe below ZnO) valence band offsets, resulting in a Type I band alignment. Growth on Cd-terminated CdTe is predicted to produce large positive offsets for a Type II alignment as needed, for example, in solar cells. To corroborate some of these predictions, thin layers of ZnO were deposited on CdTe(001) by pulsed laser deposition, and the band alignments of the resulting heterojunctions were determined from x-ray photoelectron spectroscopy measurements. Although zinc blende ZnO could not be confirmed, the measured valence band offset (2.0-2.2 eV) matched well with the predicted value. (C) 2013 American Vacuum Society.