The Fabrication And Characterization Of Ga₂O_3-x Thin Films Based Blind Ultraviolet Detector

The detectors that could detect UV light ranged from 200 to 280 nm are called Solar-blind ultraviolet?UV?photodetectors?PDs?.Solar-blind ultraviolet?UV?photodetectors?PDs?have attracted intense study interests because of its wide application areas.Ga₂O₃ have simple compositions and lattice-match substrate,so it is more hopeful to make high performance solar-blind UV detector based on Ga₂O₃ materials compared with other materials,such as MgZnO,GaAlN,SiC and diamond.Recently,The Ga₂O₃ solar-blind UV detectors have been made mainly based on three types materials,single crystal bulk Ga₂O₃,nano type Ga₂O₃ and thin film type Ga₂O₃.The performance of single crystal bulk Ga₂O₃ in solar-blind UV detector is extremely high,but The fabrication of single crystal bulk Ga₂O₃ is extremely difficult and expensive.The dark current of the detector based on Ga₂O₃ materials is lower,but the solar-blind UV responsivity of which is smaller.The growth of large area Ga₂O₃ thin films is easier and cheap.And because Ga₂O₃ thin films is also sensitive to solar-blind UV light as other type Ga₂O₃ materials,Ga₂O₃ thin film is a excellent material in solar-blind UV detection.In this thesis,Ga₂O_3-x thin films were fabricated at different pressure by magnetron sputtering,MSM structure detectors were made on Ga₂O_3-x thin films through vacuum thermal evaporation and photolithographic methods,and the effect of deposition pressure on solar-blind UV detect characteristics of Ga₂O_3-x thin films were studied.Then Ga₂O_3-x thin film was annealed under Ar and air atmosphere seperately.Effect of anneal atmosphere on solar-blind UV detection characteristics of Ga₂O_3-x thin films were studied,and relative reasonable explanations were given for associated experimental results.The main results are listed as follows:1.Ga₂O_3-x thin films were fabricated at 300 K under different pressure on sapphire substrate by magnetron sputtering.The Ga₂O_3-x thin films deposited at different pressures were constituted mainly by amorphous Ga₂O_3-x,some Ga₂O_3-x nanocrystallines were embedded inside the amorphous Ga₂O_3-x through related measurement.The solar-blind UV response of the detectors based on this type of Ga₂O_3-x thin films were high because of the strong absorb ability of Ga₂O_3-x nano crystalline,the excellent transport characteristics of amorphous Ga₂O_3-x to photo generated carriers and the much higher gain introduced by high density of acceptor interface states between amorphous Ga₂O_3-x and Ga₂O_3-x nano crystallines.The solar-blind UV response of Ga₂O_3-x detector increased when deposition pressure increased from 0.35 Pa to 0.8 Pa,which is reasoned from the stronger absorb of Ga₂O_3-x thin film with more Ga₂O_3-x nano crystallines to solar-blind UV light and higher internal gain induced by higher density of interface states in Ga₂O_3-x thin film deposited at higher pressure.While the pressure is too high?1.0 Pa?,the solar-blind UV responsivity of Ga₂O_3-x thin film decreased because the resistance function of surplus interface states to the transmission of photogenerated carrier exceed the more gain induced by increased interface states.so,the dark current was decreased at the same time,the Ilight/Idark was increased.Under 25 V bias voltage,The maximum responsivity of Ga₂O_3-x thin film deposited at 0.8 Pa reached 413 A/W at 240 nm.Under 15 V bias voltage,The dark current of Ga₂O_3-x thin film deposited at 1.2 Pa is just 1.5 × 10-8 A,and the Ilight/Idark of which reached 1.1 × 104.2.The Ga₂O_3-x thin film that deposited at 0.8Pa were annealed under air atmosphere at different temperatures,and effect of anneal temperature on UV detection characteristics of Ga₂O_3-x thin films were studied.The maximum responsivity of Ga₂O_3-x thin film annealed at 300 oC was 2.2 A/W at 25 V bias voltage,which is lower than that of as-grown Ga₂O_3-x thin film.This phenomenon is caused by the resistance of surplus Ga₂O_3-x nanocrystallines to the transmission of photogenerated carriers within annealed Ga₂O_3-x thin film and lower gain of Ga₂O_3-x thin film with smaller density of interface states.The maximum responsivity of Ga₂O_3-x thin film annealed at 500 oC was just 0.0038 A/W at 25 V bias voltage,which is reasoned from the much stronger resistance of annealed Ga₂O_3-x thin film constituted mainly by Ga₂O_3-x crystal grains to the transmission of photogenerated carriers and even much lower gain of crystaline Ga₂O_3-x thin film with even much smaller density of interface states.The dark current of Ga₂O_3-x detector decreased when the annealed temperature increased.The dark current of the detector based on Ga₂O_3-x thin film annealed at 500 oC was just 3.2×10-10 A,and the maximum Ilight/Ilark of which is 11.3.The Ga₂O_3-x thin film that deposited at 0.8 Pa were annealed under Ar atmosphere at different temperatures,and effect of anneal temperature on UV detection characteristics of Ga₂O_3-x thin films were studied under Ar atmosphere.The change in the performance of the detector based on annealed Ga₂O_3-x thin film under Ar atmosphere is similar to that of the detector based on annealed Ga₂O_3-x thin film under air atmosphere,and the Influence mechanism of anneal treatment on performance of Ga₂O_3-x detector under Ar atmosphere is also similar to that of anneal treatment on performance of Ga₂O_3-x detector under air atmosphere.The difference between two types of anneal treatment is that the there are less Ga₂O_3-x crystalline grains in Ga₂O_3-x thin film annealed at the same temperature under Ar atmosphere than that in annealed Ga₂O_3-x thin film under air atmosphere.When anneal temperature increased from 300?to 500?,The maximum responsivity of the detector based on annealed Ga₂O_3-x thin film decreased from 24.4 A/W to 0.0147 A/W under 25 V bias voltage.