THEORETICAL AND EXPERIMENTAL STUDIES OF THE ZNSE/CUINSE2 HETEROJUNCTION BAND OFFSET

We report first-principles band structure calculations that show that ZnSe/CuInSe2 has a significant valence band offset (VBO, DELTAE(v)): 0.70 +/- 0.05 eV for the relaxed interface and 0.60 +/- 0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d-Se,p level repulsion in CuInSe2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n-type CuInSe2 (112) single crystals at 200-degrees-C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is DELTAE(v) = 0.70 +/- 0.15 eV, in good agreement with the first-principles prediction.