Preparation And Optoelectronic Properties Of Mg_xZn_1-xO Ternary Compounds

Mg_xZn_1-xO Ternary compounds are a type ofâ…¡-â…¥ZnO based semiconductor material. The band gap of ZnO is about 3.3 and that of MgO is 7.8eV at room temperature. The band gap of Mg_xZn_1-xO film theoretically can be continuously adjustable from 3.3eV to 7.8eV, so that Mg_xZn_1-xO Ternary compounds have a wide application prospect in the UV, Visible emitting devices and solar blind region UV detectors. Mg_xZn_1-xO Ternary compounds become the hot spots of current research.In this thesis, Mg_xZn_1-xO thin film samples with various components were prepared on sapphire, quartz glass, Si and ceramic etc substrates by Sol-Gel spin-coating method and radio frequency magnetron sputtering (RFMS) method respectively. Components, structure and surface morphology were characterized with photoelectron energy dispersive spectroscope(EDS), X-ray diffraction(XRD) and scanning electron microscope(SEM). The properties of absorption, transmission and luminescence were studied by UV-visible spectrometer and UV-visible fluorescence spectrometer. The effects of fabrication conditions on the structure and optical properties of the film were discussed. A UV detector with MSM structure on Si (111) /Mg_xZn_1-xO was also prepared by lithography and wet chemical etching method and its properties ofâ… -â…¤and spectral responsivity were measured by hall test meter and spectral response measurement system. Mg_xZn_1-xO nanopowders were prepared by Sol-Gel method and Mg_xZn_1-xO ceramics were also prepared with the produced nanopowders. The properties of structure, luminescence, absorption and transmission of nanopowders and ceramics were characterized by XRD, UV-visible spectrometer and UV-visible fluorescence spectrometer. Main research results obtained are as follows:1. Results of film prepared by Sol-Gel spin-coating method indicate that high quality Mg_xZn_1-xO sol could be obtained under the conditions of acidic condition (pH value between 6.5-7.0), temperature of the solution at 80℃, heating rate at 2-4℃/min, stabilizer at 0.3ml/g. Better samples of film were obtained by drying the sol at 120℃, then heating it at 300℃for 30min and calcined at 600℃for lh.2. The components of the film prepared by Sol-Gel spin-coating method and the components of design should be consistent. The structure of film changes with the x value. Mg_xZn_1-xO thin film is hexagonal ZnO structure with x≤0.33 while Mg_xZn_1-xO thin film is cubic MgO structure when x≥0.5. The crystal structure of the Mg_xZn_1-xO thin film is hybrid structure of ZnO and MgO when 0.33 xZn_1-xO thin film prepared by Sol-Gel spin-coating method was mainly composite of three emission peaks near at 384nm, 443nm and 536nm respectively. Quartz glass substrate is conducive to UV light emission, Si substrate is conducive to blue light emitting and the luminescence of thin film caused by the defect levels. Improving sintering temperature is conducive to the blue emission. Annealing makes UV emission peak of the film happen blue-shift and blue-ray emission peak happen red-shift. Mg_xZn_1-xO thin films with various components and on different substrates all have characteristics of UV excitation, while excitation spectrum on Si substrate is wider. Sintering temperature and annealing have no impact on excitation spectrum of thin film. With the content of Mg increased, absorption edge of the film blue shift and band gap increased. Annealing can also increases the band gap of film.4. Results of film prepared by RFMS method indicate that high quality film samples could be obtained under the conditions of sputtering power at 300W, gas flow at 20sccm, distance of target and baffle at 10mm, distance between target and substrate at 80mm, substrate temperature at room temperature, sputtering time at 50min. Particle size of film is homogeneous and particles grow up with the sputtering time increases. The smallest average particle size of film on sapphire substrates is about 10nm and the biggest average particle size of film on Si substrate is about 40nm. So the film is nanofilm.5. Components of film prepared by RFMS method are inconsistent with the target components and the content of Mg in film should be larger than the content of Mg in the target. The component of Mg_xZn_1-xO film on Si substrate is Mg_0.59Zn_0.41O. The component of Mg_xZn_1-xO film on sapphire substrate is Mg_0.47Zn_0.53O. The component of Mg_xZn_1-xO film on quartz glass substrate is Mg_0.44Zn_0.56O. The component of Mg_xZn_1-xO film on chip-carrier substrate is Mg_0.52Zn_0.48O. The structures of Mg_xZn_1-xO film on different substrates all were the hexagonal wurtzite structure of ZnO with c-axis oriention.6. Mg_xZn_1-xO film prepared by RFMS method has a clear absorption edge. The absorption edge of thin film on sapphire substrate is located at 292nm, absorption edges of thin films on quartz glass and Si substrate are located at 298nm and absorption edge of thin film on chip-carrier substrate locates at 312nm. The average transmittance of films on sapphire and quartz glass substrate is 80%. The absorption edge and luminescence peak of films blue shift with the sputtering time increases.7. The response cut-off edge of UV detector locates at 295nm corresponded to the spectral responsivity R_λis 5.85A/W. External quantum efficiency is 2460.6%, NEP is 1.681×10¹²W, D is 5.95×10¹¹W^-1, D^* is 1.78×10¹¹ cm·Hz·W^-1. The maximum response in the solar blind region locates at 260nm and corresponding spectral responsivity R_λis 7.17A/W. External quantum efficiency can be 3421.8%, NEP is 1.365×10¹²W, D is 7.33×10¹¹ W^-1, D^* is 2.2×10¹¹ cm·Hz·W^-1.8. Powder of Mg_xZn_1-xO exist two structures as the hexagonal wurtzite of ZnO and face-centered cubic rock salt structure of MgO. Mg_xZn_1-xO powder is the hexagonal structure of ZnO when x is less than 0.20,Mg_xZn_1-xO powder is face-centered cubic structure of MgO when x is greater than 0.80. The grain of powder has gradual improvement with the growing of sintering temperature. Transmittance of Mg_xZn_1-xO ceramic prepared by produced nanopowders change with the x value.