First-Principles Studies Of P-type Doping In ZnO

ZnO is a wide band gap LED semiconductor material with extensive application prospect. However, the p-type ZnO is very difficult to obtain, which leads to its application scope restricted within narrow limits. How to fabricate the p-type ZnO, is a very important problem which attracts many people's intrests and attention. Based on enough literature at home and abroad, we have systematically researched on some problem about p-type ZnO theoretically in this thesis.Based on the density functional theory (DFT), the first principles pseudopotential method is employed to investigate mainly the following questions:Firstly, startting with the structure of ZnO, the crystal structure and the electronic band structure were analysed, and then,based on the density functional theory (DFT), the first-principles, which is applied extensively in material calculation, was introduced. Furthermore, the pseudopotential theory was presented especially. Afterwards, all kinds of intrinsical defects have been studied in detail. According to the results, it was pointed out that the zinc interstitials and oxygen vacancies stemming from excessive zinc, are the dominative source for the n-type electronic conductivity in ZnO. The following parts focuses on the N doping ZnO with comprehensive investigation and indicated that N is a good candidate element for p-type dopant in ZnO. But it needs a Zn-rich condition for the process of N doping ZnO, because the Zn-rich condition can render the formation energy the lowest. However, this is confronted a difficulty to choice: Although the Zn-rich condition is propitious to enhance the nitrogen concentration, for the lowest formation energy of N doping ZnO, meanwhile, it also favors to form the n-type electronic conductivity, which will form the compensation mechanism for N acceptors in ZnO, it weakens the effect of p-type doping. The codoping models were investigated simultaneously in this thesis, but the results haven't distinct improvement for p-type doping. Lastly, the nitrogen and hydrogen codoping models, which differ greatly from the others, were presented. In this model, the different point is that the hydrogen reside in the interstitial site, nitrogen occupy the oxygen site, which result in lower formation energy——much more lower than only N doping ZnO. This model conduce to prevent the zinc atom in interstitial and weaken the compensation role of donor versus acceptor, and it is the most effective model comparing with the other models. Finally, the application prospect in ZnO is presented in this thesis.