Band offsets at the ZnSe/CuGaSe2(001) heterointerface

Abstract

The formation of the ${\mathrm{ZnSe/CuGaSe}}_{\mathrm{2}}$ heterointerface was studied by x-ray photoelectron spectroscopy (XPS). ZnSe was sequentially grown on ${\mathrm{CuGaSe}}_{\mathrm{2}}\text{(001)}$ epilayers. In situ photoemission spectra of the Ga $\text{3d}$ and Zn $\text{3d}$ core levels as well as XPS valence bands were acquired after each deposition step. The valence-band offset is determined to be ${\mathrm{\Delta E}}_V\text{=0.6±0.1\hspace{0.05em}}\mathrm{eV}.$ As a consequence, a nearly symmetric “type-I” band alignment for the ${\mathrm{ZnSe/CuGaSe}}_{\mathrm{2}}$ heterojunction with a conduction-band offset of ${\mathrm{\Delta E}}_C\text{=0.4±0.1\hspace{0.05em}}\mathrm{eV}$ is found. Concerning the band alignment ZnSe can, therefore, be expected to be a suitable buffer material for ${\mathrm{CuGaSe}}_{\mathrm{2}}$ -based thin-film solar cells.