Research On The Properties Of ZnO Films And Its P-Type Doping

Attribute to its wide and direct band gap （3.37 eV）, large exciton binding energy （60 meV） and high radiation hardness at room temperature, ZnO is regarded as a promising material for preparation of short wavelength light emitting diodes and laser diodes with low thresholds. However, there are still some unsolved problems limiting its further application in optoelectric field. First, as-grown undpoed ZnO always show n-type conductivity, but the origin of this n-type conductivity is still controversial; Second, it has been proven to be very difficult to produce a stable and reproducible p-type ZnO films with high conductivity and mobility, which make the ZnO films fail to live up to its potential in optoelectronic devices based on pn junction; Third, it is difficult to obtain high quality ZnO films for lacking of good lattice-matched and thermal-matched substrates. According to above research difficulties on ZnO films, we will pay more attention to the origin of the n-type conductivity, p-type film based on ZnO material and related optoelectronic devices in this thesis. The details are as follows:（1） Undoped ZnO and MgZnO films were grown on a c-plane sapphire by plasma-assisted molecular-beam epitaxy technique （PA-MBE）, and subsequently annealed in water vapour and hydrogen ambient, respectively. It was found that H acts as a donor and is the principal source of intrinstic donor in ZnO films. Surface of the ZnO films can be improved by annealed in hydrogen. While annealed in water vapour, it was O not H from water vapour play an important role in the electrical properties of the annealed films.（2） ZnO:N films were grown by PA-MBE on c-plane sapphire at the different Zn temperature （TZn）. It was found that high Zn temperature is benefit for obtaining p-type ZnO films. The anomalous Raman mode at 275 cm-1 was related to substitution of N for O site （NO） and not related to substitution of N₂ for O site （N₂）O. ZnO:N films grown on a- and c- sapphire substrates, and the influence of lattice mismatch on doping efficiency of N-doped ZnO films was investigated. It was found that larger lattice mismatch is benefit for enhancing the N concentration in ZnO films.（3） p-type MgZnO:N films were obtained by PA-MBE usingδ-doping method, and the effects of the Zn₃N₂ layer on the formation and properties of the p-typeδ-doped MgZnO:N were discussed. A UV photodetector based on a heterojunction of p-MgZnO:（Li,N）/n-ZnO was fabricated. Enhancement in peak responsivity at 330 nm under back-illumination was achieved for the reduction of the surface recombination velocity and the increases of the optical penetration depth in MgZnO films.