Study On The Photosensitivity Of Graphene-lead Selenide Heterojunction

In recent decades,with the development of semiconductor technology,traditional and new semiconductor materials have received increasingly attention.As a traditional narrow-gap semiconductor,PbSe is a direct bandgap material,and its bandgap is 0.27 eV at room temperature,and it is often used in infrared?IR?detection.Due to its low carrier mobility,the application of lead selenide in the field of infrared detection is mostly based on the post-sensitization treatment of PbSe thin films to achieve good performance.Graphene is a new type of two-dimensional semiconductor material.It has many unique properties,such as extremely high carrier mobility,zero band gap,etc.It is widely used in optics,sensing and other fields.In recent years,many researchers have applied it to the infrared detection field,but due to its single-layer structure,there is only a small light absorption rate?about 2.3%?.Combining the excellent electrical properties of graphene with the sensitivity of PbSe to IR,forming a new type of heterojunction structure,with complementary advantages,and separating the photogenerated electron-hole pairs,will contribute to their wide application in the field of infrared detection.In this paper,PbSe thin films were prepared by molecular beam epitaxy?MBE?and graphene/PbSe heterojunctions were prepared.The infrared photosensitivity of the heterojunctions was preliminary explored,and on this basis,the chemical bath deposition?CBD?method was used to prepare PbSe thin films to further explore the infrared photosensitivity characteristics of the graphene/PbSe heterojunction interface.We explored the optimum process parameters for both processes and characterized the structure,morphology,composition,and optical properties of PbSe thin films.The characterization results showed that the optimal parameters for the epitaxial preparation of PbSe by MBE are:PbSe source temperature is 600°C,Se source temperature is 160°C,and substrate temperature is 200°C.Under this process condition,PbSe grows along the?200?plane orientation.The surface of the thin film sample is all PbSe-combined,and there is no impurity oxide?such as SeO4,etc.?,and it shows a Pb-rich state.When the PbSe thin film was prepared by the CBD method,we found that the temperature largely affected the quality of the thin film.The lower the temperature,the worse the crystalline quality of the film,and the PbSe grows along the?111?orientation of the crystal plane.XPS analysis showed that the PbSe films deposited under various temperature conditions were all Pb-rich,and the Se atom content also increased with the increase of the growth temperature.The SEM scan results showed that the surface of PbSe films prepared by MBE epitaxy was smoother than the CBD method,and the grain size was smaller and more uniform.The infrared transmission spectrum results showed that the optical bandwidth of the PbSe film prepared by MBE method is 0.38 eV,indicating that PbSe responds to the infrared spectrum.In addition,we also characterized the graphene's material properties.Raman spectrum showed that the ratio of the peaks'intensity of graphene(I_G/I_2D)is 0.45,and there is no D peak,which consistent with the characteristics of monolayer graphene.These results indicat that graphene made by CVD method has fewer defects,which is suitable for the production of heterojunctions.In order to characterize the electrical properties of graphene,field effect transistor based on graphene was fabricated.The mobility of graphene?hole?calculated from the transfer characteristic curve was 839.5 cm²/?V·s?.Based on the study of PbSe thin film materials and graphene,we used MBE epitaxial PbSe thin film to prepare a back gate type graphene/PbSe heterojunction phototransistor?W/L=10?m/100?m,PbSe area 50?m×50?m?.Results showed that the device has good infrared photosensitivity?the light wavelength is 1050 nm?,and the maximum photocurrent is 8?A,and the corresponding maximum responsivity is 420 AW^-1.The device showed controllable characteristics of the gate voltage,which contributes to its application in the field of low-light detection.The energy band model analysis believes that the device's variable responsivity is caused by the transfer of photo-generated holes in the PbSe layer to graphene,which could be controlled by gate voltage.When the V_gs is lower than the V_Dirac,the I_ill is bigger than the I_dark?hole accumulation?,and when the V_gs is higher than the V_Dirac,the I_ill is smaller than the I_dark?holes transferred from PbSe to graphene recombine with electrons in graphene?.