The Study On Structure, Electrical And Optical Properties Of Low-Dimensional ZnO

ZnO is a wide energy band gap (3.37eV) semiconductor with largeexciton binding energy (60meV) at room temperature. ZnO has drawnconsiderable research attentions, because of its low lasing threshold,friendliness to the environment, cheapness, and excellent photoelectricproperties. The application of ZnO in optoelectronics is hampered by someproblems that have not been solved, for example, the stable p-type ZnO is hardto fabricate, and the bandgap engineering can not meet demand.This paper has two parts, theoretical calculations and experimental study.Theoretical calculations have been made of two parts. One is study on theinteraction between O vacancies and typical p-type impurities, and the effect ofO vacancies to impurities. The other is the calculations of Al doped Zn1-xMgxO,including the lattice structure, band structure, density of state and opticalproperties. The experimental study also has two parts. One is that the Al dopedZn1-xMgxO powders are synthesized through hydrothermal. The experimentcan corroborate with the theoretical result. The other experiment is Al dopedZnO powders fabricated under different hydrothermal temperatures. The effectsof synthesis temperature and annealing are analysised. Details are as follows:(1) The calculation method based on Density Functional Theory (DFT) wasintroduced, and calculation steps of CASTEP in Material Studio were described.The functions and some parameters including cut-off energy, k-points weretested for ZnO.(2) The three different typical p-type impurities Ag, N, K are investigated from first-principle based on DFT. The lattice structure, band structure, density ofstate and formation energy of oxygen (O) vacancies are calculated under thecondition of perfect crystal and defect crystal with O vacancies, respectively.The results showed that the formation energy of O vacancies are lowest inK-doped cells, and the Ag-doped has highest hole conductivity.(3) The model of Zn1-xMgxO and Al doped Zn1-xMgxO were built. In the twosystems, the lattice structure, electronic structure, optical properties withdifferent value of x were calculated, with the value of the x is0,0.0625,0.125,and0.1875, respectively. With the increasing of the Mg content, the energy gapwere broaden, refractive index and absorption rate were decreasing. The effectsof Al doped on Zn1-xMgxO were analyzed. Carriers in Al doped Zn1-xMgxOincreases, while the optical absorption rate decreases, in this system theabsorption rate decreased with the increasing of the Mg content.(4) The Al doped Zn1-xMgxO powders were synthesized through hydrothermalmethod, and the lattice structure and optical properties were analyzed. Theexperiment can corroborate with the theoretical result.(5) The Al doped ZnO powders were synthesized through hydrothermal method.The effect of different synthesis temperatures was analyzed. The lowtemperature is beneficial to improve the utilization of raw materials and the sizeof the grain with low temperature is smaller, but the microscopic strain wasbigger than the products of high synthesis temperatures. The microscopic straincan be decreased by annealing, this can improve the quality of the products.The synthesis temperature has significant influence to the size and morphology,this lead to the difference of the UV-visible absorbance.