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 repul sion in CuInSe2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscop y. ZnSe overlayers were sequentially grown in steps on n-type CuInSe2 (112) single crystals at 200-degrees-C. In situ photoemission measurem ents were acquired after each growth in order to observe changes in th e valence band electronic structure as well as changes in the In 4d an d 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-prin ciples prediction.