Performance Study Of The Self-Powered UV Photodetectors Based On（Pb,La）（Zr,Ti）O₃ Thin Films

As an important photoelectric device,ultraviolet photovoltaic detector has been widely used in the military,medical and people’s livelihood fields.However,it must rely on external power supply to realize the optical detection behavior,which makes the photodetectors not further integrated,miniaturized and lightweight,and inevitably leads to high dark current and small switch ratio,which seriously limits the practical application of photodetectors.With the continuous development of detector technology in recent years,a new type of photoelectric device called self-powered photodetector is proposed.The common self-powered ultraviolet photodetector is a junction photodetector made of wide-band semiconductor.Its built-in electric field only exists in a very thin barrier area,which is not conducive to the separation of light-generated electron-hole pair.Therefore,the response degree and detection rate of the general junction ultraviolet photodetectors are very low,and the response speed is not fast.Different from the common wide-band semiconductor materials,ferroelectric materials will induce a depolarized electric field under the polarization of the applied electric field,which is throughout the whole ferroelectric material.Additionally,the optical voltage of ferroelectric materials is not limited by the band width of the crystal,and can be 2～4 orders of magnitude higher than the band width.This anomalous photovoltaic effect and the depolarized electric field throughout the body mean that ferroelectric thin film-based photodetectors have higher photoelectric conversion efficiency and fast response speed compared to junction photodetectors.Due to the large optical band gap（>3.1 e V）and excellent ferroelectric characteristics,（Pb,La）（Zr,Ti）O₃（PLZT）film material can be used to prepare a self-powered UV photoelectric detector.Based on this,PLZT ferroelectric film was prepared by sol-gel method and made into self-powered ultraviolet photovoltaic detector.First,the optimal film thickness of the photoelectric device was studied,and then the ferroelectric performance of PLZT film was enhanced by regulating the La element content,so as to further improve the performance of the detector.Additionally,in order to improve the photoelectric response performance of ferroelectric thin-film based optoelectronic devices in deep ultraviolet bands,amorphous Ga₂O₃/PLZT heterojunction films with different PLZT film layers and their optoelectronic devices were prepared,and their photoelectric response performance at different polarized voltages was studied.The experimental research contents of this paper are as follows:1.A series of Pb_0.93La_0.07(Zr_0.2Ti_0.8)_0.9825O₃（PLZT）films of different thickness were prepared by sol-gel method using FTO conductive glass as a substrate.The Au electrode was plated on the surface of PLZT film and FTO conductive glass,and a self-powered UV photodetector based on vertical structure was prepared,and the influence of thickness on the phase structure,surface morphology,optical properties,ferroelectric properties and photoelectric device performance of PLZT film was studied.The results show that all thicknesses of the films show pure perovskite structure with smooth and compact surface.In addition,with the decrease of thickness,the optical band gap of the film increased bit by bit,and the residual polarization strength gradually increased from 30.2μC/cm²to 40.1μC/cm².The photodetector of the 3-layer PLZT film shows the best photoelectric response performance due to its excellent ultraviolet light absorption and light-generated electron hole separation ability.At 0 V bias and+2 V polarization voltage,the responsiveness of 13.1 m A/W,normalized detection rate of 4.11×10¹¹Jones and response time t_r/t_dof 20 and 30 ms,respectively.2.The sol-gel method was used to prepare different Pb_1-xLa_x(Zr_0.2Ti_0.8)_0.9825O₃（x=0.02、0.04、0.06、0.08 and 0.1）（PLZT）films and their optoelectronic devices,and the phase structure,optical properties and ferroelectric properties of PLZT films were investigated.The results show that all the films with different La content have good crystallization characteristics.With the increase of La content,the diffraction peak corresponding to the crystal surface of（110）gradually shifts to the high angle direction,and the optical band gap of the film increases little by little.In addition,the residual polarization value of the film first increases and then decreases with the increase of La content,and the maximum residual polarization value can reach 45.3μC/cm².Among all self-powered UV photodetectors,the device exhibited the highest photoelectric response performance at a La content of 0.04.Under the 0 V bias condition,when the polarization voltage is+2 V and the irradiation wavelength is300 nm,the detector has a high light/dark current ratio（6357）and a fast response speed（12/20 ms）,with a responsiveness and normalized detection rate of 15.1m A/W and 5.04×10¹¹Jones,respectively.3.By combining PLZT ferroelectric thin films by sol-gel method,amorphous Ga₂O₃/PLZT heterojunction films and their photoelectric response properties at different polarized voltages were studied.The results show that when the number of PLZT thin film layers is 2 layers,the corresponding photoelectric device shows the best photoelectric response performance.At 0 V bias,with polarized voltage of+1.5V and irradiation wavelength of 250 nm,responsiveness up to 17.2 m A/W,normalized detection rate of 4.33×10¹¹Jones and response time t_r/t_dof 1.5 and 2 s,respectively.