Research Of The Mechanism Of Buffer Layer Crystalline On The Properties Of ZnO Films

ZnO is made up of II-VI group elements,which is a compound semiconductor material with wide band gap and has the six-party symmetric structure.The energy difference between the bottom of the conduction band and valence band at the top is3.37eV and exciton binding energy is60meV at the normal temperature.So,ZnO is expected to be applied to the wavelength of the device, semiconductor laser and detector device, etc.When ZnO films is deposited in the form of heteroepitaxial growth, the crystal structure of ZnO film present a more crystalline or amorphous for mismatch of the lattice caused by different lattice between films and substrate.Therefore,the crystal quality,luminous efficiency and the stability of heteroepitaxial ZnO films is relatively poor.Firstly,wo deposited a thinner layer of ZnO buffer layer on the substrate surface before the epitaxial of ZnO films to study the effect of high temperature annealing treatment on the buffer layer properties and the mechanism of buffer layer on the primary properties of the secondary growth films.In this paper,we deposited ZnO films on the C-Al2O3substrate directly by MOCVD and characterized with X-ray diffractometer, photoluminescence and atomic force microscope equipment to compare with ZnO films deposited on buffer layer.Afer that,a thinner ZnO film was deposited on Al2O3substrate at the same conditions of epitaxial ZnO film directly and annealing in the atmosphere of nitrogen.The crystallization was characterized by X-ray diffraction and found that the crystallization properties was improved by annealing.In addition,we got a better annealing temperature that is900℃at which the c axis orientation of growth characteristics is best.The uv peak and deep level peak intensity ratio decreased significantly as the increase of annealing temperature in the photoluminescence and when the temperature reach the1000℃,no obvious ZnO light-emitting peak could be found.Therefore, the optical properties of buffer layer could be reduced by annealing.The properties of electrical in buffer layer show high resistance state by hall,which is due to the high temperature that made ZnO decompose.so,carriers could not transmit smoothly for the effect of the grain boundary.As a result,the resistance of buffer layer had been improved.Finnally,we deposited ZnO films on buffer layer.It found that the crystallization,optical,electronic propert ies and surface maophology characteristics had been improved as the increase of annealing temperature.In addition,when the annealing temperature reach900℃, the epiaxial ZnO film has good c axis orientation and the uv peak half high width appeared a minimum. The carriers mobility is higher and the resistivity is relativelylower.Therefore, buffer layer technology can effectively improve the various properties of epitaxial thin filims and has an important influence on application and popularization of ZnO materials.