The Study Of Gallium Oxide Based Semiconductor Films And Ultraviolet Photodetectors

Gallium oxide?Ga₂O₃?,as a new type of oxide semiconductor materials,has larger bandgap,lower on-resistance and stable physical and chemical properties.So Ga₂O₃ would be widely applied in high-temperature,high-frequency,high-power electronic and ultraviolet or deep-ultraviolet photoelectric devices.In addition,various types of impurity atoms could be incorporated in the crystal lattice to change the properties of the materials,such as Si,Sn,In and Al.In this work,the?-(In_xGa_1-x)₂O₃ and Sn doping?-Ga₂O₃ thin films were deposited on c-plane sapphire substrates by Pulsed Laser Deposition?PLD?.The influences of substrate temperature,oxygen pressure and doping proportion on the properties of films were systematically investigated.In addition,the ultraviolet photodetectors were fabricated for analyzing the photoelectric properties.The main research contents and results of this paper are as follows:First,the single-crystalline?-(In_xGa_1-x)₂O₃ films were grown on the double polished sapphire substrates at different temperatures and oxygen pressures by PLD.With the oxygen pressures increased from 0.001 mBar to 0.01 mBar,the polycrystalline films were obtained,as the result of XRD measurement.As the substrate temperature increased more than 500?,the samples showed the single crystalline and the diffraction peaks of?-(In_xGa_1-x)₂O₃ films were located at the lower angle side in comparison with?-Ga₂O₃peaks.The In composition x of the?-(In_xGa_1-x)₂O₃ films would be decreased and the bandgap E_G would be broadened with the enhancement of growth temperatures or the decrement of oxygen pressures.The photoelectric properties of(In_0.08Ga_0.92)₂O₃,(In_0.05Ga_0.95)₂O₃ and Ga₂O₃ photodetectors were characterized by the photo and dark current,the typical time-dependent photoresponse and the responsivity measurements.The E_G of(In_0.08Ga_0.92)₂O₃?(In_0.05Ga_0.95)₂O₃ and Ga₂O₃ photodetectors were 4.77 eV,4.88 eV and 4.98 eV,respectively.In comparison with Ga₂O₃ photodetectors,the?-(In_xGa_1-x)₂O₃devices showed the enhanced photo and dark current,higher responsivity and more persistent photoconductivity?PPC?due to the In element incorporation,resulting in the higher conductivity,lower Schottky barrier height and more defects in the bandgaps.Second,the growth of single crystal?-Ga₂O₃ films on the double polished sapphire under the assistance of Sn element was studied by PLD.The crystal structure,photoelectric properties and chemical state of the element were investigated to characterize the influence of Sn during the film.As the Sn proportion increased over 0.7at%,the?-Ga₂O₃ films were obtained,and the epitaxial relationship of the outer surface was?-Ga₂O₃?0001?\\Al₂O₃?0001?.In addition,there was a transition layer between the substrate and the?-Ga₂O₃ film interface.What's more,with the Sn composition increasing,the thicknesses of the transition layer were decreased.The Sn atoms would be existed as Sn⁴⁺,Sn²⁺or Sn⁰,during the?-Ga₂O₃ films growth.Sn⁴⁺or Sn²⁺would weaken the accumulation of Ga₂O,and Sn⁰represents the formation of cluster in the film.The photodetectors were fabricated on the?-Ga₂O₃ films with Sn contents increasing from 0.9%to 1.2%and 1.5%.The higher dark current,photo current,and responsivity were achieved in the?-Ga₂O₃ devices due to the Sn atoms aggregation and the formation of clusters,and the bandgaps E_G of the Sn doped films were 4.81 eV?@0.9at%?,4.88 eV?@1.2at%?and 4.94 eV?@1.5at%?.