Study On Preparation And Ultraviolet Detector Of Gallium-based Wide Bandgap Semiconductor Nanowires

Ultraviolet detection technology is widely used in military and civil.Photodetector is the key of ultraviolet detection technology,which is usually based on semiconductor materials.Compared with other traditional semiconductor materials such as silicon,wide band gap semiconductor materials are more suitable for the preparation of ultraviolet detector.Gallium nitride(GaN)and gallium oxide(Ga₂O₃)are typical wide band gap semiconductors,which are good materials for preparing ultraviolet detector.Generally,GaN-based ultraviolet detector can detect ultraviolet light with wavelengths less than 365nm,but it has no selective for deep ultraviolet light.Ga₂O₃ has a larger band gap,which is more suitable for solar-blind ultraviolet detector.This thesis focuses on preparation of GaN and Ga₂O₃ nanowires and their ultraviolet detectors.The main contents of this study are as follows:(1)GaN nanowires with smooth and serrated side surface were prepared by chemical vapor deposition.The Vapor-Liquid-Solid(VLS)mechanism was used to explain the growth of the nanowires.The theory shows that the surface tension of the alloy droplets plays an important role in the growth of the nanowires.Copper nanowires were prepared by liquid-phase reduction method,and a photoconductive ultraviolet detector based on GaN nanowires was fabricated by using copper nanowires as electrodes.The detector has different response under different wavelength light illumination and has the maximum response under illumination of 365nm ultraviolet light.The dark current is 5.6n A and the photocurrent is 108n A at 5V bias.The ratio of photocurrent to dark current of the detector is about 18.3 times.(2)A solar blind ultraviolet detector based on Ga₂O₃ nanowires was fabricated.Firstly,Ga₂O₃ nanowires were prepared on silicon substrate by chemical vapor deposition,and the samples contained a small amount of Ga₂O₃ nanosheets.There are Vapor-Liquid-Solid(VLS)and Vapor-Solid(VS)mechanisms in the growth of Ga₂O₃nanomaterials.The VLS mechanism leads to the axial growth of nanowires,and the VS mechanism leads to the lateral growth of nanowires,which is conducive to the formation of nanosheet structure.Finally,a solar-blind ultraviolet detector based on Ga₂O₃ nanowires was fabricated by using Au interdigital electrode.Two back-to-back Au/Ga₂O₃ schottky junctions can effectively reduce the dark current and improve the response speed.The dark current of the detector is 0.087n A at 10V bias.Under 254 nm ultraviolet light illumination,the photocurrent of the detector is 27 n A,and the ratio of photocurrent to dark current is about 310.(3)An ultraviolet detector based on Ga₂O₃/GaN nanowires heterojunction was fabricated.GaN nanowires were deposited on sapphire substrate,and the gap region with width of about 20?m was fabricated between GaN nanowires.The ultraviolet detector based on Ga₂O₃/GaN nanowires heterojunction was fabricated.The dark current of the detector is 1.6×10^-10A at 10V bias,and it is hardly sensitive to 365nm light.The photocurrent of the detector is 2.2×10^-7A under 254nm ultraviolet illumination,and the ratio of photocurrent to dark current is about 1375.The detector has the advantages of low dark current,high responsivity and high signal-to-noise ratio.In this study,the gap was fabricated on sapphire surface during the growth of GaN nanowires,which is a new method to fabricate ultraviolet detectors based on nanowires heterojunction.