Study On Perovskite/Wide Bandgap Oxide Semiconductor Heterojunction Ultraviolet Detector

Ultraviolet detectors are widely used in biological,medical,military,environmental and other fields.With the development of semiconductor materials and semiconductor manufacturing technology,UV detectors based on wide band-gap semiconductors have become a research hotspot in UV detection.Traditional wide-band gap oxide semiconductors,such as TiO₂,Ga₂O₃,ZnO,NiO,etc.,are widely used in ultraviolet detectors,due to their various advantages,for example,different specific absorption wavelength ranges,diverse preparation processes,non-toxic and good chemical stability.However,one single semiconductor material also has its shortcomings.A short carrier life and a low mobility lead to low photocurrent and response,and internal defects lead to high dark current.This paper aims to improve the performance of a single wide bandgap oxide semiconductor ultraviolet detector by studying the heterojunction formed by a variety of perovskite materials and oxide semiconductors(TiO₂ and In_0.4Ga_1.6O₃).These perovskite materials include perovskite MAPbCl₃,PbTiO₃,CuTiO₃,and La₂Ti₂O₇.This paper mainly carries out the following research work.After forming heterojunction between perovskite MAPbCl₃ and wide bandgap oxide semiconductor TiO₂,the effect of MAPbCl₃ on the performance improvement of TiO₂ UV detector was studied.The properties of TiO₂nanorods films grown by hydrothermal method on FTO were improved.The FTO/TiO₂/MAPbCl₃ UV detector by reverse temperature crystallizationwas prepared,and the horizontal structure of perovskite film and the vertical structure of nanowire array were formed.The photogenerated electron hole pairs are effectively separated at the heterojunction interface.The electrons drift along the nanowire,and the holes drift along the perovskite direction,which effectively prolongs the carrier lifetime,reduces the recombination and improves the photocurrent.At the same time,due to the characteristics of perovskite polycrystalline domains,multiple contact depletion regions formed by scattering carriers in the dark state can effectively reduce the dark current of the device(from 1.557×10^-6 A to 2.69×10^-10 A),and thus improve the light-to-dark ratio of the device（from 87.3 to 6.607×10⁵）,responsivity and detectivity.In addition,the mechanism of high performance of TiO₂/MAPbCl₃ heterojunction UV detector is described by theoretical analysis and parameter analysis.Study the effect of PbTiO₃ and CuTiO₃ on the performance improvement of TiO₂MSM UV detector after forming heterojunction.The PN junction MSM structure UV detector of PbTiO₃/TiO₂ and the type Ⅰ heterojunction MSM structure UV detector of CuTiO₃/TiO₂ were prepared.The film by a sol-gel method has high yield,high chemical stability,and the dark current and response recovery characteristics of the UV detector with MSM structure are also superior.Contrast to characteristics of TiO₂ MSM UV detector,both dark currents were significantly reduced(from 6.849×10^-9 A to1.146×10^-11 A,and from 4.11×10^-8 A to 8.06×10^-12A,respectively),and both response and recovery times were greatly reduced（from 1.02 s and 5.35 s to 65 ms and 81 ms,and from 1.84 s and 7.35 s to 78 ms and 93 ms,respectively）.The mechanism of PbTiO₃/TiO₂ heterostructure is analyzed in detail.The spontaneous polarization of ferroelectric perovskite PbTiO₃ can deplete the photogenerated carriers of TiO₂,accelerate the separation and transport of electron-hole pairs,greatly improve the carrier collection efficiency and thus accelerate the response recovery characteristics of the device.CuTiO₃/TiO₂ constitutes the type I heterostructure.According to the band structure of Au/TiO₂/CuTiO₃/TiO₂/Au under 0 V bias,biased in dark and under illumination,the potential well effect of CuTiO₃ with type I heterostructure on photogenerated carriers is analyzed,and the photogenerated electron-hole recombination inside TiO₂is effectively inhibited.Finally PbTiO₃/TiO₂ and CuTiO₃/TiO₂ UV detectors have low dark currents and faster response recovery properties.In order to develop the best overall performance of the UV detector,not only including the dark current and response recovery properties,but also the photocurrent,responsivity and light-dark current ratio and other properties.To study the effect of La₂Ti₂O₇ on the performance of UV detector of single oxide semiconductor formed by layer perovskite La₂Ti₂O₇ and wide band gap oxide semiconductor heterojunction.La₂Ti₂O₇/TiO₂ heterojunction MSM UV detector and La₂Ti₂O₇/In_0.4Ga_1.6O₃ heterojunction MSM UV detector were prepared.Contrast to characteristics of TiO₂ and In_0.4Ga_1.6O₃ MSM UV detectors,both photo-dark ratios were improved（from 266to 200943,and from 2349 to 79308,respectively）,and both response recovery time is shortened（from 1.84 s and 7.35 s to 1.07 s and 2.48 s,and from 6.23 s and 4.81 s to 1.54 s and 2.35 s,respectively）.Detailed mechanism analysis of La₂Ti₂O₇/TiO₂ and La₂Ti₂O₇/In_0.4Ga_1.6O₃heterostructures were carried out.The difference between theoretical and actual Schottky barriers was explained.The oxygen vacancy formed by In-doped Ga₂O₃ can increase the carriers and improve the photocurrent and responsivity.The interlayer space of La₂Ti₂O₇ crystal structure contributes to the efficiency of separating photogenerated electron hole pairs and more charge carriers.Moreover,the netted TiO₆ octahedral spatial structure and the micro-nanorod-like morphology are conducive to carrier transport,thereby improving the efficiency of photon absorption and the external quantum efficiency of the detector.In this paper,a variety of wide bandgap perovskite semiconductors are developed to improve the performance of traditional oxide semiconductor UV detectors.The improvements in dark current,photocurrent,response recovery speed,gain,responsivity,detectivity,noise and external quantum efficiency of the devices are analyzed.This paper provides a valuable reference for the development prospect of wide bandgap perovskite semiconductor materials in ultraviolet detection.