Band alignment at the Cu₂ ZnSn (S_xSe_1-x) ₄ /CdS interface

Energy band alignments between CdS and Cu2 ZnSn (S xSe1-x) 4 (CZTSSe) grown via solution-based and vacuum-based deposition routes were studied as a function of the [S] / [S+Se] ratio with femtosecond laser ultraviolet photoelectron spectroscopy, photoluminescence, medium energy ion scattering, and secondary ion mass spectrometry. Band bending in the underlying CZTSSe layer was measured via pump/probe photovoltage shifts of the photoelectron spectra and offsets were determined with photoemission under flat band conditions. Increasing the S content of the CZTSSe films produces a valence edge shift to higher binding energy and increases the CZTSSe band gap. In all cases, the CdS conduction band offsets were spikes. © 2011 American Institute of Physics.