Spectra And Flexible Photoelectricity Of 2D Inse And Heterojunction By Pulsed Laser Deposition

With deeper researches in the field of two-dimensional?2D?semiconductors,layered semiconductors have also shown more and more amazing physical properties.However,a basic but widespread problem always exists in this field:how to get large-area 2D materials.Common methods for obtaining 2D materials,such as chemical vapor deposition or mechanical exfoliation,are difficult to get samples larger than a few hundred microns in size.In order to solve this problem,we deeply explored the application of pulsed laser deposition?PLD?system in synthesis of large-area 2D indium selenide?InSe?materials.As one of III-V 2D semiconductors,InSe has attracted wide attention due to its excellent photoelectric properties and ultra-high electron mobility.The PLD system can easily obtain large area InSe films with a size of a centimeter.We have realized the synthesis of large-area 2D InSe films by PLD at different temperatures.We found that the suitable temperature for InSe by PLD covers the range from 350oC to 600oC.The broad temperature range requirement undoubtedly enriches the variety of substrate choices,also brings the possibility of forming heterojunctions in combination with other materials.The XRD and Raman system analysis shows that the?-phase InSe film has good crystallinity.According to the XPS test technology,the stoichiometric ratio of In to Se is 1.08:1,which is very close to the theory.The contact between semiconductor films and metal electrodes often deeply affects the electrical performance of the device.However,there is a large Schottky barrier of about 0.7 eV between Au electrodes and InSe films,which are used widely in devices.In order to decrease the barrier between metal and semiconductor,we designed and implemented a self-assembled CuInSe₂/InSe lateral heterojunction.Through the introduction of Cu atoms,a new substance CuInSe₂ is formed,and the energy band structure between the film and the metal copper electrode is modulated by the heterojunction.Analysis of the stoichiometric ratio shows that CuInSe₂ region is copper poor and indium rich.This deviation from the ideal stoichiometric ratio causes the CuInSe₂ region to appear as a heavily doped n-type semiconductor.We explored the distribution of CuInSe₂/InSe heterojunctions by Raman Mapping and SEM,and there were obvious differences on both sides of the junction of the heterojunction.In order to investigate the energy band distribution between the heterojunction and the metal,we used KPFM to acquire the surface potential change of the heterojunction near the copper electrode,then obtained the band diagram of the heterojunction.There is a weak Schottky barrier between copper electrodes and the CuInSe₂ regions,and the quasi-ohmic contact between the heterojunction film and the copper electrode is approximately 0.05 eV.Compared with Au/InSe samples,it was found that the CuInSe₂/InSe heterojunction has better linear I-V characteristics.Further,a built-in electric field is formed in the heterojunction from CuInSe₂ to InSe.The existence of the built-in electric field makes the photocurrent of CuInSe₂/InSe heterojunction device be about 4 times that of Au/InSe device.In the optical switch curve,as the optical power density of different surfaces increases,the switching ratio of the heterojunction gradually increases to about 40 times.Finally,we explored the photoelectric effect of the CuInSe₂/InSe heterojunction photodetector in a flexible state.The externally applied stress has a greater effect on the dark current of the device.Under large compressive stress,the dark current of the heterojunction is gradually suppressed,so the switching ratio is improved.