Band offsets at the ZnSe/CuGaSe₂(001) heterointerface

The formation of the ZnSe/CuGaSe₂ heterointerface was studied by x-ray photoelectron spectroscopy (XPS). ZnSe was sequentially grown on CuGaSe₂(001) epilayers. In situ photoemission spectra of the Ga 3d and Zn 3d core levels as well as XPS valence bands were acquired after each deposition step. The valence-band offset is determined to be ΔEV=0.6±0.1 eV. As a consequence, a nearly symmetric "type-I" band alignment for the ZnSe/CuGaSe₂ heterojunction with a conduction-band offset of ΔEC=0.4±0.1 eV is found. Concerning the band alignment ZnSe can, therefore, be expected to be a suitable buffer material for CuGaSe₂-based thin-film solar cells.