Research On Fabrication And Photoelectric Properties Of (In_xGa_1-x)₂O₃ Films

Ultraviolet（UV）detectors have attracted much attention because of their wide application in military and civilian fields.According to different detection wavebands,UV detectors can be divided into visible-blind UV detectors and solar-blind UV detectors.Ga₂O₃ is a wide bandgap semiconductor material widely used in the solar-blind UV detection field.However,the bandgap of undoped Ga₂O₃ is too large（the common structure is about 4.9 e V）,which makes Ga₂O₃ detectors difficult to detect the whole solar-blind UV region and easy to cause signal loss.(In_xGa_1-x)₂O₃is a ternary wide bandgap semiconductor material obtained by In element doping Ga₂O₃.With the increase of In content,the bandgap of(In_xGa_1-x)₂O₃ can be adjusted continuously from 3.7 e V-4.9 e V,which effectively solves the problem faced by Ga₂O₃.However,at present,the application of In doping in the field of Ga₂O₃ solar-blind UV detection is far from extensive,partly due to the insufficient research on material preparation,the controversial mechanism of In doping on the photoelectric performance of detectors,and the lack of design and performance research of heterojunction self-powered detectors.Based on the above problems,the main research contents of this dissertation are as follows:(In_xGa_1-x)₂O₃ films were prepared on sapphire substrates by magnetron sputtering.The effects of sputtering pressure and annealing temperature on the structural and optical properties of(In_xGa_1-x)₂O₃ films were investigated.As the sputtering pressure increased,the V_O concentration decreased and the sputtering particle energy reduced,leading to the grain size of(In_xGa_1-x)₂O₃ films increasing first and then nearly invariant and then decreasing.The decrease of V_O concentration also leads to the increase of optical bandgaps and the ratio of intensity with a green light to blue light emission.After annealing treatment,(In_xGa_1-x)₂O₃ films grown at room temperature were transformed from an amorphous structure to a polycrystalline structure.The increment of annealing temperature increased the particle size of the films,but they also produced non-（2?01）-oriented particles,leading to the poor preferred orientation.The increase of the annealing temperature also decreased the In content and the compressive stress,which caused the increase of the optical bandgaps.(In_xGa_1-x)₂O₃ films grown at high temperature were polycrystalline structures.The increment of annealing temperature increased the grain size of(In_xGa_1-x)₂O₃ films.But if the annealing temperature was too high,the grain size decreased,or the homogeneity deteriorated.Considering the grain size and uniformity of the(In_xGa_1-x)₂O₃ films grown at high temperature,800°C is the best annealing temperature.The effects of In content on the structural and optical properties of(In_xGa_1-x)₂O₃films were investigated.With the increase of In content,the crystal structure of(In_xGa_1-x)₂O₃ films was gradually transformed from a monoclinic phase to a mix-phase in which the bixbyite phase and the monoclinic phase coexisted until a bixbyite phase was formed.Due to the differences in the substitutional impurities,the increase of In content led to the decrease of the grain size of monoclinic structure(In_xGa_1-x)₂O₃ films,and the increase of the grain size of bixbyite phase(In_xGa_1-x)₂O₃ films.The optical bandgaps of(In_xGa_1-x)₂O₃ films decreased linearly with the increase of In content.MSM structure detectors based on(In_xGa_1-x)₂O₃ films were fabricated.The influence of In content on photoelectric performance of(In_xGa_1-x)₂O₃ film detectors was discussed.It was found that monoclinic(In_xGa_1-x)₂O₃ film detectors had excellent solar-blind UV detection performance,and In doping could regulate the responsivity of monoclinic(In_xGa_1-x)₂O₃ film detectors by changing the grain size.The(In_0.23Ga_0.77)₂O₃/(In_0.67Ga_0.33)₂O₃ heterojunction self-powered solar-blind UV detector was fabricated by adjusting the energy band structure of(In_xGa_1-x)₂O₃films with In element.At zero bias,the responsivity of the detector was 5.78 m A/W,and the detectivity was 1.69×10¹¹ cm Hz^1/2 W^-1,which had excellent self-powered detection performance.The(In_0.23Ga_0.77)₂O₃/(In_0.67Ga_0.33)₂O₃ heterojunction detector also had excellent solar-blind UV spectral selectivity due to the inhibition effect of the high carrier concentration of the(In_0.67Ga_0.33)₂O₃ film on the internal electric field width.This detector provided a new idea for the design of self-powered solar-blind UV detectors based on(In_xGa_1-x)₂O₃ heterojunction.In addition,the influence of the thickness of the Au electrodes and(In_0.23Ga_0.77)₂O₃ films on the responsivity of the heterojunction detectors was also investigated.The optimal thickness of the Au electrodes and the(In_0.23Ga_0.77)₂O₃ films was determined as 12.9 nm and 350 nm.The FTO/(In_0.23Ga_0.77)₂O₃/Spiro-Me OTAD organic-inorganic hybrid hetero-junction self-powered visible-blind UV detector was fabricated by the synergistic effect of(In_0.23Ga_0.77)₂O₃ and Spiro-Me OTAD films.The detector had excellent photoelectric detection performance from 200 nm to 400 nm.At zero bias,the responsivity of the detector was 0.63 m A/W,and the detectivity was 5.4×10¹⁰ cm Hz^1/2 W^-1.There was a double built-in electric field in the(In_0.23Ga_0.77)₂O₃ film,which promoted the separation and transmission of photogenerated electron-hole pairs,resulting in a fast response speed of the detector.The response time was only0.02 s.Moreover,the rejection ratio(R₄₀₀/R₄₅₀)of this detector was 125,indicating this detector had excellent UV-visible spectral selectivity.Finally,the resolution of solar-blind UV and non-solar-blind UV wavebands was successfully realized by using the“UV filtering”function of FTO,which provided a new idea for the design of wide-response self-powered visible-blind detectors with waveband resolution.