H. Salehi - physics Department, Shahid Chamran University, Ahvaz, Iran
S.M. Baizaee - physics Department, Vali-e-Asr University, Rafsanjan, Iran
Azam Soltani Mohammadi - physics Department, Vali-e-Asr University, Rafsanjan, Iran

Most of the group II–VI binary compound semiconductors crystallize in either cubic zinc blende or hexagonal wurtzite structure where each anion is surrounded by four cations at the corners of a tetrahedron and vice versa[1]. This tetrahedral coordination is typical of sp3 covalent bonding nature, but these materials also have a substantial ionic character that tends to increase the bandgap beyond the one expected from the covalent bonding. ZnO is a semiconductor whose ionicity resides at the borderline between the covalent and ionic semiconductors[2]. Upon compression above 9.0 GPa, a phase transition to rocksalt-type (B1) structure (space group Fm3m), with an increase in coordination number from 4 to 6 [3]. ZnO is one of the most studied materials in the group of II–VI semiconductors because of its wide band gap 3.44 eV [4] and its bulk exciton-binding energy (60meV)[5], which is larger than the room-temperature thermal energy. In this paper we studied density of states in cubic phase of ZnO semiconductor. Calculation on this structure have been carried out using FP-LAPW method in framework Density functional theory, DFT, and by using WIEN2K pachage [6]. We found that there is hybridization between 2p states in O atoms and 3d states in Zn atoms that it cause band gap estimate. For improve band gap in rock-salt phase of ZnO we used engel-vosko [7] approximation. Also, we calculated electron density of states in (110) and (100) planes that showed ionic future for this phase of ZnO and good agreement was obtained compared to the other results[2].