PREDICTION AND OBSERVATION OF II-VI-CUINSE2 HETEROJUNCTION BAND OFFSETS

First-principles band structure calculations show that II-VI/CuInSe2 h eterojunctions have significant band offsets which challenge the tradi tional explanation of device operation. In the case of ZnSe, these lar ge valence band offsets demonstrate the failure of the ''common anion rule''. This is traced to a stronger Cu,d-Se,p level repulsion in CuIn Se2 than the Zn,d-Se,p repulsion in ZnSe. Formation of the ZnSe/CuInSe 2 and CdS/CuInSe2 heterojunctions were studied by synchrotron radiatio n soft x-ray photoemission spectroscopy. The II-VI overlayers were seq uentially grown in steps on both CuInSe2(112) single-crystals and poly crystalline thin-films. In-situ photoemission measurements were acquir ed after each growth in order to observe changes in the valence band e lectronic structure as well as changes in the appropriate core lines. Results of these measurements reveal that the offsets are in good agre ement with the first-principles predictions and that the traditional d evice model with DELTAE(C) < 0 must be abandoned.