Study Of The Preparation And Characteristics Of MgZnO Thin Films Grown By MOCVD

In recent years,much attention has been given to wide band gap semiconductors for the wide uses in blue and ultraviolet light emitters and detectors. The materials for emitting blue light which have been fabricated have obvious shortcomings now. A mass of defects appear in ZnSe laser at high temperature, so its lifetime is very short. For achieveing GaN,the equipment is expensive and growth is difficult. ZnO is a wide band-gap semiconductor(3.37 eV at room temperature)with the high exciton binding energy of 60 meV. The crystal structure and lattice constant of ZnO are similar to those of GaN. The ion radii of Mg2+ (0.57 ?)and Zn2+ (0.60?)are so close that Mg2+ can replace the location of Zn2+ in ZnO film partially. MgZnO thin films can be used not only as barrier layers for ZnO active layer, but also directly as an ultravioler light emission material.Various deposition techniques has been used to prepare MgZnO thin films such as pulsed laser deposition (PLD),sputtering,molecule beam epitaxy (MBE),metal-organic chemical vapor deposition (MOCVD), and so on . In this thesis, high quality MgZnO films had been grown on sapphire substrate by MOCVD. The effects of various preparation condition on the properties of MgZnO film were discussed in detail. P-MgZnO films were obtained on GaAs substrate by As diffusion. P-MgZnO/n-ZnO heterojunction light emitting devices were fabricated based on this method, and the characteristics of this series of device were investigated.MgZnO alloy thin films were prepared on c-plane sapphire substrates by MOCVD. The effects of the growth temperature, the flux of oxygen, the thickness of buffer layer and the anneal in O2 on the properties of the films were analyzed. The results of XRD and PL showed that the crystallinity of MgZnO film grown at 610℃were the best. Under lower temperature, the growth speed of MgZnO was rapid, a great deal of gas atoms were adsorbed by the surface. It affected the mobility of atoms, which resulted in the crystal quality degrading. Under higher temperature, because MgZnO film had decomposed before the reaction happened, the speed decreased with the increasing of the temperature. The flux of oxygen had an important effect on the structural properties and surface morphology of MgZnO film. The qualities of MgZnO film became best when the flux attained 200sccm. The thicknesses of ZnO buffer layers were adfusted by controlling deposition time. When the thicdness was 20nm, the intensity of (002) diffraction peak in XRD pattern was the strongest, and the peak value began to reduce when the thickness increases continually. This phenomenon was maybe caused by the decrease of the nucleation density of ZnO muclei. It implied that the buffer layer thickness of 20nm was optimized. The crystal quality of the films annealed in oxygen had been changed largely. The PL spectra showed that the deep level emission peak became stronger after the annealing heat treatment. It showed that the deep level emission intensity was related to the concentration of vacant Zn defects.The p-MgZnO films were grown by the doping As atoms diffused into MgZnO film from GaAs substrate. We found that As-O band is broken and the arsenic exists in the state of AsZn-2VZn acceptor complex after annealing. X-ray photoelectroscopy (XPS) shows that As atoms have already diffused into MgZnO film, and the hall-measurement has indicated that the ZnO film is P-type. The P-MgZnO/n-ZnO heterojunction showed a diode I-V characteristic and can emit light under forward bias.