Study Of ZnO Based Ultraviolet Photoelectric Detective Material

As an important Ⅱ-Ⅵ semiconductor oxide, ZnO has a wide and direct band gapof3.37eV（RT）, corresponding to the ultraviolet photon energy. With its properties suchas high chemical and thermal stability, strong ability of anti-radiation damage, abundant,low electron induced defects, etc., ZnO is suitable for fabricating high-performanceUltra-violet detector. Alloying ZnO films with doped Mg or Cd potentially permits theband gap to be controlled, thus it can be used to constitute a quantum well orsuperlattice structure for optoelectronic devices to increase their optoelectronicperformance, therefore, band gap engineering is conductive to promoting thedevelopment of practical and high performance ZnO-based optoelectronic devices.Especially for ZnO based UV photodetector, ZnO ternary alloy can adjust detectiveband to the solar-blind region, UV photodetector developed on this basis can be usedwidely in the military and civilian field.In view of the above, we modulate band gap of ZnO with doping method, makingthe optical band gap of the ZnO-based ternary alloy to be above4.4eV, to developZnO-based photoelectronic detector which can be used for solar-blind band ultravioletdetection; Also by the doping controlling technology, we develop ZnO-basedhetero-structures, which can be applied to high-performance UV photocathod. Thedetailed contents and innovations of the thesis are as follows:1. Mg、Cd、Al doped ZnO ternary alloy thin films were prepared by sol-gel method,and the micro-structure, electrical and optical properties of the alloy films were studied,the doping efficiency and the effect of band gap control was analyzed, rule of doping tocontrol the band gap of ZnO was obtained. Mechanism of the band gap modulation wasdiscussed from the perspective of Zn3d binding energy variation.2. Al_xZn_1-xO（AZO） alloy film were deposited by RF magnetron sputteringmethod, the effect of Al-doping concentration on the structural and optoelectroniccharacteristic of AZO films were researched. Results of the studies have shown that:ZnO wurtzite structure were disappeared when Al concentration increased to20at%,thus in the solid solubility of Al-doping is less than20at%. AZO film has a formation of compound nanostructure with new crystalline phase when the Al concentration is30at%;particles of thin films were getting smaller with increasing of Al content, and resistivityincreased substantially; the optical band gap of AZO films is broadened obviously bychanging the Al concentration, the optical band gap of30at%Al concentration sampleis broadened to4.43eV.3. The effect of oxygen atmosphere on the electrical conductivity of AZO alloyfilms were researched, through analyzing its micro-structure and optical properties, theresults were obtained as follows: Addition of a small amount of oxygen can improveand enhance the c axis preferred orientation of the crystal structure; but the filmsdeposited in pure Ar atmosphere possess the lowest resistivity and special build-inelectric field, and Raman and SEM results indicated the existence of two types of thecrystalline orientation, normal and parallel to c face respectively; the addition of oxygencontent in the gas mixture leads to formation of more insulating films; the filmdeposited in pure Ar atmosphere exhibits a larger blue-shift of the optical absorptionedge.4. Optoelectronic response performances of AZO alloy thin films were researched,the results show that: Al doping can depress formation of oxygen vacancy defect in theZnO films, and insulation characteristic of AZO films is enhanced while Alconcentration is increasing, which help realize a low dark current, it means thelight-dark current ratio can be improved, particularly, increasing Al concentration caninhibit the slow adsorption and desorption reactions of oxygen, thereby enhancing theresponse speed of the device. AZO UV detectors with fast response speed showsymmetric nonlinear characteristics, which were applied to Chua’s circuit throughelement replacement, a triple-scroll optoelectronic chaotic attractor can be generated inthe modified Chua’s circuit.5. The effect of Al doping on the surface barrier and work function of AZO filmswere researched, experiments proved that height of surface contact barrier reduced withincreasing Al concentrations of AZO alloy films by testing C-V characteristic. From thetheoretical calculations and experimental I-V-T fitting method, the surface workfunction of pure ZnO and5at%Al-doped ZnO thin films were obtained, the valuedecreased by0.09eV and0.098eV respectively. The above results show that Al dopingcaused Fermi level moved into the conductive band, then AZO films possess a smaller surface barrier, resulting in electrons more easy to escape from the surface.6. Al_xZn_1-xO thin films were used for realizing negative electron affilitive（NEA）UV photocathod, and fabricating vacuum phototube, the light-dark current ratio is morethan two orders of magnitude. Using high conductive AZO films as transparentconductive bottom electrode, cation vacancy dominant AZO nano-crystalline film wereinduced grown on the bottom electrode. So the AZO hetero-structure was obtained bydoping control technology, which achieved energy band modulation and good UVemission properties due to good interface between electrode layer and cathode layer,after actived by Cs, the test results show that: the dark current is0.2nA, and thephotoemission current is220nA under254nm UV irradiation, light-dark current radio isabout103order of magnitude.