Preparation And Performance Research On GaN Based Heterojunction Ultraviolet Photodetectors

Ultraviolet（UV）photodetectors have a broad range of applications,including in fields such as astronomy,missile warning,and non-visual secure optical communication.Based on the photoelectric effects,photo-induced carriers are generated in semiconductor materials under light illumination,and the conversion of light-to-photoelectric signals can be achieved under the external or built-in electric fields.Although current commercially available silicon-based photodetectors have mature manufacturing processes and are relatively low-cost,they require expensive external filters to achieve UV detection and are deficient in several aspects such as device structural complexity and sensitivity.The third-generation semiconductors,such as GaN,have attracted widespread attention from scholars due to their intrinsic UV absorption window and excellent material properties.And GaN-based UV photodetectors offer several application advantages,including simple structure,fast response,and high temperature resistance.To further improve the performance of GaN-based UV photodetectors and develop novel applications,this thesis focuses on optimizing GaN crystal quality and optical absorption,constructing heterojunctions,and regulating energy bands.The primary research areas include:1.Research was conducted to investigate the preparation of porous GaN through a photo-assisted electrochemical wet etching method.To enhance the light absorption efficiency and reduce defects,planar GaN was transformed into porous structures using a UV light-assisted electrochemical etching method.The two critical factors of etching voltage and etching time were regulated to analyze the morphology of the porous structures and their optoelectronic properties.The results showed that under 10 V,5 min etching conditions,the porous GaN surface was uniform,dense,and had high porosity.It exhibited better crystal quality and lower defect density compared to planar GaN.Moreover,the reflectivity of the porous GaN（3.9%）was reduced by a factor of approximately 10 when irradiated with 370 nm UV light,significantly enhancing the light trapping capability compared to planar GaN（38.8%）.2.Research was conducted on exploring the preparation and performance of MoO₃/porous GaN heterojunction narrow-band UV photodetectors.The heterojunction was formed through thermal evaporation of a MoO₃ layer onto porous GaN films,resulting in narrow-band UV photodetectors,and leading to a high responsivity of 198 m A/W and the optimized response with a full width half maximum of only 10 nm.3.Research was conducted on GaN-based MIS tunneling heterojunction UV photodetectors using crystalline/amorphous HfO₂ insulating layers.The study constructed Ag/HfO₂/GaN MIS junction-based UV photodetectors by introducing a thin interfacial layer of HfO₂ to the MS structure.The HfO₂ films were prepared using a simple solution method,with the crystalline/amorphous films obtained by controlling the annealing temperature.Results showed that the crystalline state of the film had a significant impact on the performance of the MIS junction UV photodetector,with the UV response of the device with an amorphous HfO₂thin film being much better than that of the crystalline one.The MIS junction UV photodetector with a 13.2 nm amorphous HfO₂ layer inserted displayed the best photoresponse performance,with a responsivity of 198.4 A/W at-2 V bias and 330 nm incident light,and an external quantum efficiency of over 10,000%.The ultrahigh photoelectric gain observed can be attributed to the impact ionization of hole carriers within the amorphous HfO₂ lattice under the strong electric field formed by the tunneling heterostructure.In summary,this thesis proposes a filterless,narrow-band heterojunction UV photodetector by optimizing the crystal quality and optical absorption properties of GaN through photo-assisted electrochemical etching technique,which expands the functionality of GaN-based photodetectors.Additionally,an Ag/amorphous Hf O2/GaN MIS tunneling heterojunction UV photodetector with high photocurrent gain is proposed,and the carrier transport mechanism is systematically investigated,providing a new approach for the development of high-performance UV photodetectors.