Preparation And Study On The Characteristics Of Amorphous Ga₂O₃ Thin Films And Their Solar-Blind Ultraviolet Photodetectors

Due to the high wavelength selectivity and strong anti-interference ability,solar-blind ultraviolet（UV）photodetectors have broad and important application prospects in many fields such as flame detection,missile early warning and confidential communication.solar-blind UV photodetectors based on wide bandgap semiconductor materials are receiving more and more attention due to their small size,all solid state,intrinsic solar-blind,and strong anti-radiation and anti-interference ability.Among many wide-band-gap semiconductor materials,wide-band-gap oxide semiconductor materials represented by Ga₂O₃ not only has relatively low cost,stable thermal stability and chemical stability,but also has a band gap width of about 4.5eV-4.9 eV,which is very suitable for solar-blind UV detection,so it is considered to be a very ideal material for the preparation of solar blind UV detectors.Compared with the traditionalβ-Ga₂O₃ thin film,amorphous Ga₂O₃（a-Ga₂O₃）material not only has the same excellent photoelectric characteristics,but also has some unique advantages such as,a low growth temperature,not require a lattice matching substrate,simple preparation equipment and process,and low cost.Then,it attracts much attention in the field of flexible photovoltaic devices and large-area photovoltaic devices.However,research on amorphous Ga₂O₃ solar-blind UV detectors is still in its infancy.The intrinsic defects related to oxygen vacancies seriously affect the photoelectric detection performance of amorphous Ga₂O₃ materials.Aiming at the shortcomings and key problems of amorphous Ga₂O₃ solar blind UV detectors,this paper uses atomic layer deposition（ALD）to implement amorphous Ga₂O₃ thin films and their solar blind UV detectors,and their photoelectric detection performance is studied.The effective regulation of oxygen vacancy defects was achieved by annealing the material under the oxygen atmosphere,and its solar-blind UV detection performance was significantly improved,and the related mechanism was clarified.The main results obtained are as follows:（1）In this thesis,the a-Ga₂O₃ thin film prepared by ALD method was annealed under the oxygen atmosphere.The effects of annealing temperature on the crystal structure,optics,composition,thickness,and surface morphology of the film were studied.And we found the thickness,surface morphology,and light absorption characteristics of the film hardly change with the change in annealing conditions.When the annealing temperature is not higher than 500°C,the sample remains amorphous.And the film will be gradually transformed intoβ-Ga₂O₃,when the temperature is increased.Interestingly,as the annealing temperature increasing,the oxygen vacancy defects of the film are gradually repaired,showing a trend of gradually decreasing.It is proved that this method can effectively reduce the oxygen vacancy defects in the amorphous Ga₂O₃ material,laying a material foundation and theoretical basis for the preparation of high-performance solar blind UV detectors.（2）A metal-semiconductor-metal（MSM）structure solar-blind UV detector based on an amorphous Ga₂O₃ thin film was implemented,and the effect mechanism of oxygen vacancy defects in the thin film on detection performance of the device was studied.We found that as the annealing temperature increased,the dark current and response time of a-Ga₂O₃ solar-blind UV photodetectors were significantly reduced.Although the responsivity of the solar-blind band has decreased to some extent,the reduction of the responsivity in the visible band is more significant,which lead to the UV/visible suppression ratio significantly improved.The comparative study results of material and device characteristics show that the reduction of oxygen vacancy defects is the core reason for the performance of a-Ga₂O₃ solar blind UV photodetectors improved.The performance parameters of the 500°C annealed device（dark current=9.43 pA;response speed=150 ns;suppression ratio=2.74×10⁵;responsivity=1.34A/W）are significantly better than those reported for similar devices.（3）A self-powered dual-band UV detector based on a-Ga₂O₃/p-GaN heterojunction was realized for the first time.And the detection performance of the device was improved in an unbiased condition by using grating-like electrode structure and annealing treatment.We use molecular beam epitaxy（MBE）to grow high-quality p-GaN thin films,and then use ALD equipment to grow amorphous gallium oxide thin films on p-GaN layers at low temperatures.The sample was annealed at 500°C under the oxygen atmosphere and the a-Ga₂O₃/p-GaN heterojunction self-powered dual-band UV detector was constructed.Under unbiased conditions,the responsivity spectrum of the device shows two distinct response bands around 258 nm and 368 nm,with peak responsivity of 68.3 mA/W and 41.8 mA/W,respectively.The detector responsivity to the solar-blind ultraviolet region is basically unchanged with the change of light intensity.