Research On Preparation Of Ga₂O₃ Nanorods And Ultraviolet Detection Performance

The solar-blind ultraviolet detection technology has attracted more and more attention due to its advantages of low environmental noise,strong anti-interference ability,and high sensitivity.It has been used in various fields such as short-wave communications,missile warning,fire detection,biomedicine,and astronomical objects.Ga₂O₃,as a semiconductor material,owns a band gap of 4.4?5.3e V and thus its corresponding response band is located in the solar-blind ultraviolet region.At the same time,it has the advantages of various preparation methods,relatively low cost,and high stability,which naturally promotes it to become an outstanding candidate material in the field of solar-blind UV detection.Based on the current research status of Ga₂O₃solar-blind ultraviolet detection,this paper will gradually carry out research in accordance with the three steps of material growth,device design,and performance improvement.The research contents are given as follows.Aspects of material growth include:(1)Without introducing other heterogeneous seed layers,the two-step hydrothermal method was used to overcome the high nucleation barrier between the substrate and the solution cluster.The densely grown Ga₂O₃nanorods were prepared on the Si(100)substrate.Different hydrothermal conditions were set to study the growth process.It was proposed that the ethanol introduced in the first hydrothermal treatment played an important role,and the principle explanation was made from the perspectives of the crystal growth process,the classical thermodynamic theory and the surface tension of the solution.(2)Set the concentration gradient to study the influence of the two precursors of gallium nitrate and HMT on the size of Ga₂O₃nanorods prepared on FTO substrate,and realized the control of the size of Ga₂O₃nanorods.Through the characterization of crystal plane changes and crystal structure analysis,The mode of construction for Ga₂O₃crystal through the two precursors was explained,and the optimal growth conditions were proposed.(3)The annealing temperature gradient was set to study the transformation process of Ga OOH to Ga₂O₃prepared on FTO substrate,and the critical annealing temperature for structural transformation and the annealing range for the coexistence of the structure were obtained.The process of dehydroxylation has been veryfied during the transformation of Ga OOH to Ga₂O₃.Aspects of device design include:(1)The MSM solar-blind detector was fabricated based on Ga₂O₃by optimizing growth conditions on the FTO substrate.With the help of the back-to-back dual Schottky barriers,the dark current of this device was suppressed with an advantage in performance indicators related to dark current,R_maxwas 2.58×10^-1m A/W and D*reached 1.05×10¹¹Jones,indicating that the device could eliminate interference and accurately detect weak solar-blind signals.However,it was proved that there were many vacancies and defects inside the material,and the electron-hole transport process was trapped and released by the trap state,resulting in a very slow response speed.The rise and fall time were 45.8s and 16.0s.(2)Based on the Ga₂O₃on the FTO substrate,an improved PEC solar-blind detector was prepared.By redesigning the structure and function of the counter electrode,it not only exerted the advantages of the PEC detector,but also overcame the"ultraviolet filtering problem"enabling this type of device to detect solar blind signals below 300nm.The device obtained a high photocurrent response under 0V bias,R_maxwas 1.37×10^-1m A/W,and achieved linear detection of light power.Due to the existence of the built-in electric field,the electron holes were separated faster and the nanorods structure increased the contact surface area with the electrolyte,resulting in rapid response with rise/fall time of 0.42s/0.25s.Aspects of performance improvement include:(1)Using the two-step hydrothermal method,Al₂O₃was introduced to form a novel tree-like branched Ga₂O₃@Al₂O₃heterojunction structure with Ga₂O₃.The detection performance was also studied by the improved PEC devices.Compared with pure Ga₂O₃,Al₂O₃didn't affect the detection range of Ga₂O₃.All performance indicators of heterojunction devices was significantly improved.The R_max/R₄₀₀and photocurrent density have both increased by 100%,PDCR has reached 370%of the former.Through the analysis of the energy band structure,the Al₂O₃coated on the outside prevented the recombination loss caused by the overflow of photogenerated electrons from the semiconductor to the electrolyte.The tree-like branched structure formed by the hydrothermal method enhanced the absorption of photons and accelerated the hole to the electrolyte,causing the rise/fall time to be less than 0.1s.(2)According to the results of the material growth research stage,the annealing temperature was set to realize the preparation of Ga OOH@Ga₂O₃heterojunction.It is found that the Ga OOH@Ga₂O₃heterojunction has more accurate solar-blind detection characteristics,and R_max/R₃₀₀is improved by 430%compared with Ga₂O₃,but the performance index related to response intensity was obviously inferior to the latter.Through the analysis of the energy band structure,Ga OOH protected by the core layer of Ga₂O₃played a pure solar-blind detection function,but the conduction band from the outer Ga₂O₃was lower than that of Ga OOH,which caused the photogenerated electrons in Ga OOH to overflow into the electrolyte.