The First-Principles Study Of Electronic Structure And Properties Of ZnO

ZnO is a very promising material for blue and ultraviolet light-emitting devices, gas sensors, surface acoustic wave devices, piezoelectric devices, high temperature mico-electronic devices and photoelectron devices and so on. Many investigations have been focusing on it in the field of photoelectronics. At present, althought tremendous theoretical and experimental investigations have been done on electronic structure, optical properties, suefacs and inteface of ZnO, there are lots divarications about accurate properties of electronics and optics. So it is necessary for one to use the first principles method to explore. Electronic structures, doping, optical properties, bulk modulus and electronic structures under strain were investigated by using a first-principles ultra-soft pseudo-potential approach of the plane wave based upon the Density Functional Theory (DFT) using the CASTEP package of Materials Studio in this thesis. The main contents are as the following:1, We have studied the bulk properties of the wurtzite ZnO such as lattice parameters, band structure, bonding structure, difference charge density, density of state, and partial density of state. The calculated results indicate that ZnO is a direct wide band gap semiconductor material. The bottommost conduction band and the top of valence band are located in the Γpoint with direct gap 3.37 eV in the Brillouin zone.2, The polarization matrix elements of the medium have been calculated precisely, the energy loss spectra, the dielectric functions, reflectance spectra, refractive index and extinction coefficient and other parameters have been given. Furthermore with electronic structure information of ZnO and theory of electron inter-band transitions, the dielectric spectra and reflectance spectra are recognized. The calculated results also enable more precise monitoring and controlling during the growth of ZnO materials as possible.3, The electronic structure and optical properties of ZnO under strain have been calculated and the strain effects have also been studied. The band gap of ZnO isbroadened with the increasing strain. The results indicate that Zn-0 bond becomes shorter, and the valance bands shift towards the low energy while the conduction bands towards high energy with increasing strain. In addition, the peak in band is cracked slightly, the band gap turns wider and the Zn3d—O2p hybridization is enhanced.4-, We have researched on n-type, p-type and p-type codoping for ZnO. The properties of n-type are simulated and the results indicate that there are lots of carrier in the bottom of conduction band which improved the conductivity of semiconductor higely. With regarde to p-type doping, the calculated results reveale that ZnO material with the incorparation of Vgroup impurities (N^ P, As^ Sb) bring deep acceptor levels in the band gap, and the carriers (hole) are localized near the top of the valence band. But the codoping calculations indicate that the acceptor level shifts toward the lower-energy region and shallow acceptor level, which was boarded and showed delocalized characters, is formed.