Investigation On Lateral Photovoltaic Effect Of Metal Chalcogenide Semiconductor Heterojunctions

Metal chalcogenide semiconductor materials have attracted great interest in recent decades because of their unique optical and electrical properties.These excellent properties also make them candidate materials for solar cells,sensors,photodetectors（PDs）,and non-volatile memory devices.The lateral photovoltaic effect（LPE）is a new type of photoelectric effect.Because of its special linear dependence between the light response signal and the illumination position,it can be developed as a position-sensitive detector（PSD）.This detector can accurately detect tiny displacements below millimetres and is used in precision optical alignment such as biomedical applications,robotics,process control,position information systems,and so on.However,from previous reports,most existing PSDs are based on traditional semiconductor materials,which have some problems,such as a narrow spectral response range,mainly restricted to the visible region,a relatively lower position sensitivity,and limited tuning solutions,which limit their important applications in many fields.In this thesis,metal chalcogenide semiconductor materials including lead selenide（Pb Se）,silver selenide（Ag₂Se）,and bismuth telluride（Bi₂Te₃）were taken as research objects,and their LPE and various performance parameters and tuning methods as PSDs in Si-based heterojunctions were systematically studied.The sensitivity and response speed of the devices are significantly improved by reasonable material design,optimisation of the interface energy bands,and carrier transportation in both longitudinal and transverse directions.In addition,coupling of the pyroelectric and photovoltaic effects is proposed to improve the LPE,which not only enhances the response and sensitivity of the devices but also greatly expands their spectral response range.The main research content and results are as follows.1.The LPE of Pb Se/Si heterojunction with different film thicknesses was investigated under nonuniform illumination and zero bias voltage.By adjustment of the built-in electric field of the heterojunction,the longitudinal separation and transport efficiency of the carriers at the heterojunction interface were optimised.With the change in irradiation wavelength,the maximum lateral photovoltage（LPV）of 50 m V,position sensitivity of 190 m V/mm,nonlinearity of less than 4%,response time of～40/105μs were obtained under 1064 nm illumination.The linearity of the optical response changed with wavelength,which demonstrated its potential application in novel PSDs.The intrinsic mechanism of heterojunction photoresponse affected by laser power and switching on/off frequency was also discussed.Devices with different electrode distances were designed to achieve a working size of up to 5mm.These results provide a reference for the development of high-performance,broadband,self-powered PSDs based on the Pb Se/Si heterojunction.2.A novel Ag₂Se/Si heterojunction based on pyroelectric property of Ag₂Se film was fabricated to study the coupled mechanism of the pyroelectric effect and the photovoltaic effect,in order to improve the performance of the heterojunction photoresponse.Adjusting the structure of the interfacial energy band of the heterojunction and controlling the transport process of the carriers.The pyro-phototronic effect greatly improved the photoresponse performance of the Ag₂Se/Si heterojunction.Responsivity and detectivity increased from 3.04m A/W and 1.67×10¹⁰ Jones to 43.32 m A/W and 1.75×10¹¹ Jones,respectively,which increased by 1425%.The ultra-fast response time of 64/62μs was achieved.More importantly,the photoresponse range was extended to 1550 nm,which is beyond the optical absorption range of the Ag₂Se film and the Si substrate.3.We further developed the PSD based on the LPE of Ag₂Se/Si heterojunction and investigated its lateral photoresponse performance.In the wideband range from visible to near-infrared,the LPV exhibited excellent linear dependence with laser position.Due to the pyroelectric properties of the material,the pyroelectric polarisation charge accelerated the effective transport and rapid separation of the carriers in both longitudinal and transverse directions.Under 1064 nm near-infrared light illumination,the LPV increased from a steady state value of 0.86 m V to a transient value of 15.5 m V,which increased by 1797%.The rise/fall time was reduced to 3/5μs.The coupled mechanism of the pyroelectric effect and the photovoltaic effect was explained by the variation of the band structure of the p-n junction,which not only explains the working mechanism of improving the photoresponse performance of Ag₂Se/Si heterojunction based on the pyro-phototronic effect,but also provides a feasible method for designing and optimising broadband and high-performance optoelectronic devices.4.Bi₂Te₃ thin films were fabricated by the PLD technique and Bi₂Te₃/Si heterostructure was prepared.The carrier separation and transport efficiency in the heterojunction were studied.The laser position and wavelength dependence of the LPV response were analysed.It was found that the 10-nm-thick Bi₂Te₃ film exhibited the best heterojunction photoresponse characteristics,with an LPV and position sensitivity of 12 m V and 34 m V/mm,respectively,at the optimal response wavelength of 671 nm.Furthermore,a four-stage dynamic photoresponse behaviour of the pyro-phototronic effect was observed in the Bi₂Te₃/Si heterojunction,which enhanced the LPV output performances.Doping Se at the Te site improved the phonon and electron transport properties of the Bi₂Te₃ film,resulting in an increase in the heterojunction photovoltage response and position sensitivity to 220 m V and 550 m V/mm,respectively,and an expansion of the photoresponse range to the near-infrared region at 1550 nm.The results indicated that Bi₂Se_0.3Te_2.7/Si heterojunctions have great potential for high-sensitivity broadband photodetectors.This work expands the application scope of metal chalcogenide semiconductors,providing not only scientific basis for a deeper understanding of LPE and new tune methods,but also technical support for designing and developing self-powered photodetectors with high performance,broadband,and ultrafast response.