Research On ?-Ga₂O₃ Based Photodetectors And Related Devices

As the“clairvoyant”for human beings to explore and perceive the world,the photodetectors play an extremely important role in military and civil fields and have a wide range of applications,such as missile guidance,fire detection,medical health and energy detection,etc.?-Ga₂O₃ material is III-VI groups wide-bandgap oxide semiconductor with the direct bandgap.The bandgap is about 4.9 e V,which makes?-Ga₂O₃ material has a breakdown field of up to 8 MV/cm,4 times larger than Ga N material's Balijia figure of merit and excellent solar-blind ultraviolet response characteristics.And?-Ga₂O₃ material has very good thermal stability and radiation resistance.These characteristics have made?-Ga₂O₃ material becomes a new hotspot of wide bandgap semiconductor materials in recent years,and is considered to be one of the four major development directions of wide-bandgap semiconductors in the future.Therefore,the research and exploration of?-Ga₂O₃-based photodetectors and related devices are particularly important.In this paper,the?-Ga₂O₃-based heterojunction ultraviolet photodetectors and the related devices are constructed based on the vertical?-Ga₂O₃ nanowire arrays and?-Ga₂O₃ film.The specific research contents are as follows:(1)The condition window for preparing vertical?-Ga₂O₃ nanowire arrays by thermal oxidation was explored.The vertical?-Ga₂O₃ nanowire arrays were realized for the first time,and the graphene/vertical?-Ga₂O₃ nanowire heterojunction solar-blind ultraviolet photodetectors were constructed.By setting the oxidation temperature and oxidation time gradient,the optimal condition for preparing vertical?-Ga₂O₃ nanowire arrays was obtained.Combining graphene with the excellent optical and electrical properties to form a transparent conductive electrode and the graphene/?-Ga₂O₃ nanowire heterojunction,the graphene/vertical?-Ga₂O₃ nanowire heterojunction solar-blind ultraviolet photodetectors were achieved.And the working principle of heterojunction was explained through the energy band diagram.The results showed that the photodetectors had a strong response peak at the wavelength of 258 nm with the responsivity of 185 m A/W.And the ratio of the responsivity at 258 nm to 365 nm reached 3×10⁴,showing the excellent UV detection capability and anti-noise ability.The rise time and fall time of 9 ms and 8 ms respectively alse indicated that the photodetectors have excellent response speed and stability.(2)The vertical?-Ga₂O₃/Ga N composite nanowire arrays were prepared to realize the high-performance wide-band ultraviolet detection by controlling the thermal oxidation process,and the thermal oxidation model of Ga N nanowire was proposed.Aiming at explaining the oxidation process of Ga N nanowire,a reasonable oxidation model was proposed to analyze the transition process from the single crystal Ga N nanowire to the"polycrystalline"structure?-Ga₂O₃/Ga N composite nanowire.By changing the gas atmosphere and oxidation time in the thermal oxidation process,the oxidation process of Ga N nanowire was controlled to prepare the vertical?-Ga₂O₃/Ga N composite nanowire arrays and related detectors for the first time.Because of the low conduction band barriers and high valence band barriers in the?-Ga₂O₃/Ga N heterojunction,there were a large amount of gain in the photodetectors.The photodetectors realized the high performance wide-band ultraviolet detection with an ultra-high responsivity exceeding 550 A/W and detectivity exceeding 3.34×10¹³ cm·Hz^1/2·W^-1 in 278-366 nm ultraviolet band.(3)The thermal oxidation mechanism of Al Ga N nanowire and the deep ultraviolet detection characteristic of the oxidized nanowire were explored.A series of temperature and time gradient experiments were set up to explore and verify the transformation mechanism of the actual oxidation process of Al Ga N nanowire.The vertical Al Ga ON nanowire arrays were prepared,and graphene is combined to form heterojunction of the deep ultraviolet photodetector.Comparing the photodetectors before and after oxidation,it is found that the Al Ga N nanowire photodetectors had a response peak at the wavelength of 276 nm with a responsivity of 253m A/W.After oxidation at 700?for 1 h,the Al Ga N nanowire was converted to Al Ga ON nanowire.Due to the addition of O components,the bandgap of the nanowire becomes larger.And the response peak of the Al Ga ON nanowire photodetectors shifted to the ultraviolet direction,moving to 242 nm,and the responsivity increased to 726 m A/W,successfully achieving deep ultraviolet detection below 250 nm wavelength.(4)The solar-blind ultraviolet-infrared dual-band photodetectors based on black phosphorus/?-Ga₂O₃ heterojunction were proposed and constructed.The traditional two-dimensional material directional transfer technology had been improved.The black phosphorus film with a size of hundred microns was directionally transferred to the active area on the surface of the?-Ga₂O₃ material,and the black phosphorus/?-Ga₂O₃ heterojunction was prepared for the first time.The solar-blind ultraviolet-infrared dual-band photodetectors realized solar-blind ultraviolet and infrared detection at the wavelengths of 238 nm and 1015nm with the responsivity of 88.5 m A/W and 1.24 m A/W,respectively.At the same time,in view of the energy band structure of black phosphorus/?-Ga₂O₃ heterojunction,the working mechanism under different bias voltage and light conditions was studied in depth.(5)We proposed a new etching technology“self-reactive etching(SRE)”for?-Ga₂O₃material without plasma etching damage,and explored its etching effect and feasibility.Combining the mechanism of self-reactive etching,the optimal SRE condition of?-Ga₂O₃ film was explored by adjusting the size of the Ga source in molecular beam epitaxy.And the etching speed of 0.07?/s was achieved.In order to quantitatively compare the etching effect between traditional inductively coupled plasma(ICP)etching and SRE,MOSCAPs devices treated with different etching methods were prepared.The results showed that the interface state density(D_it)of the SRE?-Ga₂O₃ device is an order of magnitude lower than that of the ICP etched device,reaching 10¹² cm^-2.And the interface morphology after SRE was better with a roughness of about 0.263 nm,and it still maintained a clear atomic step morphology.In addition,in order to verify the practical feasibility of the?-Ga₂O₃ SRE technology in the field of power electronic devices,we fabricated trench?-Ga₂O₃ Schottky barrier diodes using the SRE method.The current density and the switching ratio of the devices reached 1620 A/cm² and 10¹⁰ at the forward biased of 3 V,respectively.