First-principles Study Of P-type ZnO Surfaces

Zinc oxide is a direct wide band gap of3.4eV which has a large excitonbinding energy of60meV at room temperature. Due to these, it has a significantadvantage for applications in optical devices.In order to obtain a b etter performanceof ZnO, doping ZnO with various elements has been a popular technique, such asN-B, N-Mg, N-Ag. Specially rare earth (RE)-and transition metal (TM)-doped ZnOsystems show interesting optical and magnetic properties, which do not have inundoped ZnO. Simultaneously, Its surfaces have been widespread used as activecatalysts and intensively researched both experimentally and theoretically.In this paper, using the first-principles calculations method based on the densityfunctional theory, we mainly investigated the things below:1) The crystal structure, electronic structure and optical properties of ZnO dopedwith various concentrations of Er were investigated. The calculated results showthat with the increase of concentrations of Er, the volume of ZnO system isexpanded. Simultaneously, the band gap of ZnO with dopant system becomesbroad. However, the conductivity of system is enhanced with the decrease of Erconcentration. On the other hand, We calculate the optical properties ofZn0.9815Er0.0185O. A new peak is observed in the low energy region. This is mainlycaused by Er doped.2) The geometrical structure, electronic structure, and optical properties of ZnO lowindexs surfaces and the surfaces doped Ag elements were investigated with themethods of first-principles. The calculated results show that the conductivity ofthe ZnO (0001) surface becomes stronger, showing the electrical properties ofmetal. The band gap of ZnO(0001) surface becomes broad. Due to the holes isintroduced in crystal, it can make ZnO (0001) surface is more easier for p-typedoping and higher hole concentration. Th Fermi of ZnO(1010) andZnO(1120)surfaces have entered the forbidden band after the relaxation. On the other hand, we find that the first layer with Ag doping is the most stable on theZnO(0001) surface.3) we present a study for Mg-doped superlattices ZnO. We find that the volume ofsuperlattices ZnO is reduced, while the band gap is extended. The dielectricfunction peaks of superlattices ZnO become smaller in the low-energy region.Interestingly, we further find Superlattices ZnO has great geometrical stabilitydue to the electrostatic potential of the doped layer is smaller than that of pureZnO...