Theoretical And Experimental Study On Structure And Optical Properties Of Ga₂O₃Compound System

Monoclinic gallium oxide （β-Ga₂O₃）, is a vital wide-bandgap semiconductor （Eg=4.5～5.0eV） and possess outstanding thermostability and chemical stability. It has numerousapplications in high temperature gas sensor, electroluminescent display （TFEL）, opticallithography, reflection-deducting coating of GaAs, solar cells, transparent electrode inultraviolet photoelectric devices and many other fields. However, there is weak conductivityfor intrinsic β-Ga₂O₃. To optoelectronic properties, much effort has been devoted to thedoping researches. The n-type β-Ga₂O₃with the resistivity of7.92×10^-2.cm has beenprepared in experiment. But the study of p-type doping is lagging notably. In order to achievethe progress from passive device to active device, the research of p-type β-Ga₂O₃isundoubtedly important. Meanwhile, it is also significant to adjust the bandgap of β-Ga₂O₃based material with the purpose of improving versatility of β-Ga₂O₃in making optoelectronicdevices.Theoretically, the effects of Zn substituting different Ga sites in β-Ga₂O₃and the Zndoping concentration on the structural stability, electronic structure and optical properties ofZn-doped β-Ga₂O₃are studied by the first-principle calculations. It indicates Zn ions are moreinclined to substitute the four-coordinate Ga ions and the thermostability decreases with theintroduction of Zn. There is higher degree of covalence between four-coordinate Ga and itsnearest neighbor O atoms but it displays ionic bonding characteristic between the Zn as wellas six-coordinate Ga and their nearest neighbor O atoms. The formation of the shallowacceptor levels indicates Zn-doped β-Ga₂O₃is a typical p-type semiconductor. With theincrease of Zn doping concentration, the acceptor levels shift to deep energy levels directiongradually and occupied O2p states near the top of valence band decrease, which can be usedto explain the decrease of optical absorption and reflectivity in near infrared region. However,because Zn doping doesn’t change the basic band structure of β-Ga₂O₃, there is no notablechange of optical absorption and reflectivity in ultraviolet region.In experiment, multilayer β-Ga₂O₃/ZnO thin films are grown on UV transparency quartz（JGS1） substrates by alternate sputtering of high purity Zn （99.99%） and sintered β-Ga₂O₃（99.99%） targets using the DC reactive and RF magnetron sputtering technique, respectively.The Ga₂O₃-ZnGa₂O₄composite thin films are obtained by post-annealing at1073K subsequently. The crystal orientation, surface morphologies, optical transmittance andphotoluminescence spectra of the samples are characterized using X-ray diffraction （D/MAX2500V）, atomic force microscopy （Veeco DI AFM）, double beam spectrophotometer（TU1901） and fluorescence spectrometer （RF-5301）, respectively. The results show ZnOsublayers have diffused and reacted with the β-Ga₂O₃to form the new compound spinelZnGa₂O₄（Eg=5.2eV） with post-annealing. The optical bandgap of as-prepared multilayerfilms can be tailored continuously with changing the thickness of β-Ga₂O₃sublayers. Thebandgap of post-annealing films is enlarged further with post-annealing process.