| Zinc oxide (ZnO) is a new multifunctional compound semiconductor of II-VI group, with a wide direct band-gap of 3.37eV and a high exciton binding energy of 60meV at room temperature. Compared with GaN, it has many similarities in the crystal lattice characteristics and the band structure, and has photo-electric properties which may compare, moreover, it also has a higher exciton binding energy as well as the low growth temperature, therefore, it was considered to be a new kind of photo-electric material in shortwave length as GaN, and becomes a popular topic of semiconducting material scientific research domain. However, from 1996, stimulated UV emission of Zn0 thin film at room temperatwe was reported for the first time, it has passed more than ten years by now, but the short wave length photoelectric such as the ZnO base light emitting diode and the light emitter diode apparatus had still not achieved the practical level. One of the most important reasons is that the reliable and reproducible technique to grow high quality p-type ZnO is not found yet.Regarding these reasearch background, and based on the density functional theory (DFT), we take the first principles as research technique to investigate natural ZnO and doped ZnO, specifically include the following four aspects:Firstly, we study the geometric structure of the natural ZnO, through the analysis of the band structure, the total density of states and partial density of states, we know that ZnO is a direct wide band-gap semiconductor, which presents n-type conductivity, the computed results also indicate that the zinc calking is the main difficulty in p-doping.Secondly, to explore the relationship between the micro-structure and the macroscopical optical response, we calculate the dielectric function, refractive index, reflectance spectra, absorption spectra, the energy loss function and other optical properties in detail. By comparison, the resultse obtained by our calculations are in good agreement with other theoretical results and experimental data.Then, by analysing the properties of the n-type ZnO doped byⅢgroup atoms (B,Al,Ga,In), We found that there are a lot of carrier in the bottom of the conduction band, which causes the improvement for conductivity of the ZnO system. When doped with different concentration of Al, following the increase of the concentrations, the whole band drift to the lower-energy, and the Fermi level move into the conduction band, appear greatly limited. Our crystal constants, obtained from the doped geometry structure, are close to the experimental datas, which shows that our computed result is credible.Lastly, we have researched on p-type doping and p-type codoping for ZnO, by doped with different concentrations of N and codoped with N and Al, respectively. Our calculations shows that N-doped is difficult to achieve p-type doping for ZnO because of the self-compensation, while codoped with N and Al can effectively improve the solubility of the acceptor N and the hole concentration of ZnO system, then form a shallow acceptor level near the top of valence band, which is very helpful for p-type doping for ZnO. Of course, it provide the theory basis for making ZnO thin film in experimental methods. |
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