The study of electronic structure and absorption coefficient of ZnTe:O alloys: A GGA+U method

In this study the electronic structures and absorption coefficient for highly mismatched ZnTe_1-xO_x alloys have been investigated on the basis of the GGA+U approximation. It is found that an isolated intermediate band (E_-) is formed within the band gap of ZnTe by the incorporation of low content of O (x < 0.0625) into ZnTe. In the range of the low O content, the variation of E_- and E₊ is in agreement with the theoretical prediction by the well-known band anti-crossing model. As the O content x exceeds 0.0625, the E₊ energy position decreases and intermediate band (E_-) cannot exist in isolation states, which is consistent with the experimental results but in contrast to the band anti-crossing model. The chemical bonding pictures show that the intermediate band states are mainly caused by the antibonding states that are formed through the hybridization of a localized O 2s state and some localized Zn 3d4s4p states. The calculated absorption coefficient exhibits an obvious enhancement within the ZnTe:O bandgap, which indicates the formation of intermediate states can effectively make use of low energy photons to improve the conversion efficiency of final solar cell based on ZnTe:O materials.