Growth And Electronic Structure Study Of Gallium Selenium

As a kind of infrared nonlinear optical crystal with good performance, GalliumSelenium can realize laser frequency conversion from mid-IR to far IR and further toterahertz regions. In this dissertation, GaSe polycrystals are composed in single-zonemethod at980℃, GaSe monocrystal is grown in Vertical Bridgeman method and theelectric structure of the crystal is studied with the help of Material Studio5.0software.For synthesis, single-zone method is adopted.We conduct thermodynamic research onthe synthesis of GaSe polycrystal, which can verify that the reaction GaSepolycrystalline synthesis is spontaneous, equilibrium constants is6.95×10~8, chemicalreaction is thorough under reaction conditions(980℃). Furthermore, because of highsaturated vapor pressure of selenium, we design the synthesis ampule by the theoreticalcalculation. The reasonable ampule could prevent the occurrence of explosion in theprocess of the synthesis. In addition, through the Ga-Se binary phase diagram analysis,the starting materials for the synthesis: Ga and Se should be sealed in a transparentfused quartz ampule in stoichiometric portions. But selenium is volatile, which maycause the deficiency of selenium in synthesized polycrystalline. We respectively usestoichiometric and selenium-rich polycrystalline synthesis method and analyze thepolycrystalline quality by means of XRD and XRF. we conclude the optimum ratios ofraw materials are about0.2wt%Se-rich.For the growth, Vertical Bridgeman technology is adopted. After the testing andanalysis by means of the XRD, Raman spectrum along the cleaved cross-section ofGaSe single crystal perpendicular to (004) plane, we conclude that the properties of theis GaSe single crystal. With the help of spectrophotometer and fourier transform infraredspectra, optical transmission tests conducted both in the UV and in the visible rangeindicate GaSe crystal transmitted between0.63to20micrometer, transmissionefficiencies of around50%. In addition, by using the chemical etching method, the maindefects of the monocrystalline GaSe include twin crystal, inclusions and dislocation.Hardness and elastic modulus of GaSe crystal are0.048GPa,1.734GPa by usingNanoindentor, respectively.Using plane wave pseudopotential method based on the density functional Theory underlocal density approximation, with the assistance of CASTEP software package of theMaterial Studio5.0software, the band structure and state density of GaSe crystals arecalculated and analyzed. Meanwhile, we forecast some optical properties of GaSecrystal, refraction, reflection, extinction and absorption included. Combined with theband structure and state density figures, it is known that optical spectrum was caused by the reason that the electron jump from the valence bands of Se-4s,4p to the conductionbands of Se-4s,4p or Ga-4s,4p.