Study On The Fabrication Of InGaO/Ga₂O₃ Thin Film Transistors By Using Magnetron Sputtering And Their Application In Ultraviolet Photodetection

Deep ultraviolet photodetectors are widely used in missile guidance and early warning,environmental pollution monitoring,optical communication and other field.The traditional deep ultraviolet photodetectors are usually two-terminal structure.In contrast,the three-terminal thin film transistor（TFT）deep ultraviolet photodetectors have the characteristics of good controllability,high sensitivity and low dark current,which is one of the most important development directions of deep ultraviolet photoelectric detection technology at present.Gallium oxide（Ga₂O₃）,as an ultra-wide band gap semiconductor material,has good stability and high deep ultraviolet absorption coefficient,making it very suitable for solar blind（200-280 nm）ultraviolet photoelectric detection applications.However,the growth conditions of high-quality Ga₂O₃ materials are relatively harsh,and the mobility of Ga₂O₃ thin films prepared by low-cost methods such as sol-gel and magnetron sputtering is usually low,which makes it difficult to directly use as the active layer of TFT.Due to the large ion radius and 4f¹⁰5s⁰ shell electronic structure of In³⁺,the amorphous indium gallium oxygen（InGaO）alloy films formed by In₂O₃ and Ga₂O₃ can achieve high migration,but inevitably reduce the solar blind UV selectivity of the detector.In this paper,the idea of using InGaO as a electron transport layer and Ga₂O₃ as a light absorption layer is proposed.The InGaO/Ga₂O₃ TFT photodetector is constructed by magnetron sputtering method.The regulation law and physical mechanism of the active layer thickness on the electrical and optical detection performance of devices are studied.The specific research contents are as follows:（1）Preparation and Study on photoelectric properties of InGaO TFT.Firstly,the active layer thickness of InGaO TFT was optimized.When the thickness of the InGaO layer increases from 5 nm to 30 nm,the migration of TFT first increases and then decreases,the threshold voltage first decreases and then increases,and the optical responsivity first increases and then decreases.This is because both free carrier concentration and vertical resistance increase with the increase of the active layer thickness,which jointly restrict the electrical properties of the TFT.When the thickness of InGaO layer is 20 nm,the mobility of the device is 36.9 cm²V^-1s^-1,the threshold voltage is 12.5 V,and the peak responsivity is 2099.49 A/W under the illumination with the wavelength of 300 nm.Secondly,the thermal stability of InGaO TFT photodetector was studied.During the process of increasing the heat treatment temperature from 100℃to 400℃in an air environment,the migration of InGaO TFT first decreased and then increased,and the optical responsivity first decreased and then increased.Through X-ray photoelectron spectroscopy（XPS）analysis,it was found that the reason may be that after low-temperature treatment,the film will absorb impurities in the air,resulting in the reduction of carrier concentration;higher temperature treatment will inhibit the above adsorption process,and then the device performance will gradually recover.（2）Study on the electrical properties regulation and application of InGaO/Ga₂O₃ TFT in solar blind ultraviolet opticaldetection.The regularities of the thickness of InGaO and Ga₂O₃layers on the electrical properties and optical response performance of TFT were studied.When the thickness of Ga₂O₃ layer is 50 nm and the thickness of InGaO layer is increased from 1 nm to 10 nm,the migration of InGaO/Ga₂O₃ TFT first increases and then decreases,and the threshold voltage first decreases and then increases.When the thickness of InGaO layer is 5 nm and the thickness of Ga₂O₃ layer increases from 5 nm to 270 nm,the migration firstly increases,then decreases and then increases.The optical responsivity first increases,then decreases and then increases with the thickness of Ga₂O₃ layer,and the optical response wavelength shifts from 275 nm to 260 nm.When the thickness of InGaO/Ga₂O₃ is 5/30 nm,the mobility of TFT is 23.1 cm²V^-1s^-1,the threshold voltage is-2.0 V,and the peak responsivity under the illumination of 260 nm wavelength is 8837.76 A/W.The energy band structure at the interface of InGaO/Ga₂O₃ was investigated by XPS and absorption spectrum.Theoretical analysis results show that there is a valence band order of 0.50 e V between InGaO and Ga₂O₃,which limits the migration of some holes from InGaO layer to Ga₂O₃ layer,resulting in a gain effect and improving the responsivity of InGaO/Ga₂O₃ TFT detector.