Structural and electronic properties of hydrogen doped Wurtzite ZnO

We have carried out comprehensive studies on the various types of hydrogen doping including, interstitial and substitutional (for oxygen) position (H-i, H-O), H-O + H-i, and oxygen vacancy plus interstitial hydrogen (V-O + H-i) complexes using DFT + U calculations. The effect of H-i, H-O, H-O + H-i, and V-O + H-i dopants on structural and electronic properties of Wurtzite ZnO at 0.020, 0.0625, and 0.125 nH/nZn concentrations, were studied. We found that cell parameters and volume of the supercells decrease in H-i, H-O, and H-O + H-i defects, whereas these values increase in the V-O + H-i case. Bader analysis shows that H ion locates at V-o(+2) in H-O doping and it also places beside V-O(0) in V-O + H-i. Furthermore, the H-O + H-i complex is a H-2 molecule that is almost neutral, electrically inactive and is trapped in V-o(+2). So, it seems that this complex is an appropriate model for formation of H-2 molecule at high temperature. ZnO band gap is slightly influenced by Hi in all concentrations while, H-O has prominent effect on increment of it which is consistent with experimental results too. In addition, it is shown that growth of H-doped sample under O-poor condition leads to improved optical properties which is applicable in transparent conductive oxide devices. It is predicted that band gap of hydrogen doped samples will decrease by annealing due to trapping of H-O by Hi and formation of H-2 molecule. Finally, hydrogen beside oxygen vacancy can create two deep levels, decreasing the optical band gap and shifting absorption edge to lower energy, which leads to a red shift and possible interest in photocatalytic applications. (C) 2017 Elsevier B.V. All rights reserved.