Study Of The Photoelectric Characteristics Of Based On The Doping-enhanced WSe₂ Nano-film And Related Heterojunction

Tungsten selenide(WSe₂)is one of the important members of transition metal sulfides(TMDCs).It has a similar layered structure and is easily peeled off into a single layer WSe₂two-dimensional crystal,which has excellent photoelectric properties due to its band gap changing from a bulk indirect band gap(1.2 e V)to a wide direct band gap(1.64 e V).Since the stripping method is difficult to obtain large area films suitable for devices while the synthesis method can easy obtain large area and high quality films but hard accurately control the number of layers,at the same the band structure of WSe₂changes again into indirect band gap with the increase of layers,lead to low photoelectric conversion characteristics.The main purpose of this study is to prepare multi-layer WSe₂films with simple and efficiently method,then doped with Er³⁺,Zn²⁺,Er³⁺and Zn²⁺co-doped to improve the optical absorptivity and photoelectric conversion efficiency of WSe₂films.Further,we studied the photoelectric characteristics of WSe₂related heterojunction because the van der Waals heterojunction formed by double or multi-layer TMDCs stacking with excellent photoelectric properties,which provides an experimental basis for further application of WSe₂in field effect transistors and photovoltaic photodetectors.The detailed studies as follows:1.The WSe₂films were deposited on silicon wafers by thermal evaporation.The surface morphology,structure,light absorption characteristics,photoluminescence spectrum and surface electrical characteristics of the samples were investigated.Having optimized the experimental conditions,it was found that the WSe₂films has better crystallinity and high electron mobility of 2.125×10²cm²·V^-1·s^-1prepared at 400?.And the photocurrent of the WSe₂film is 3 times higher than of the dark current,showing that the film has good photoelectric response characteristics.2.The WSe₂film was doped with Er³⁺,Zn²⁺,and Er³⁺and Zn²⁺together respectively,and the influence on photoelectric characteristics was analyzed.Firstly,after doped Er³⁺,the film has the highest the surface mobility of 9.86×10²cm²·V^-1·s^-1,which is more than 4times that of the undoped film.The photocurrent is about 3 times larger than that dark current under irradiation on the surface of the film with a light of 25 m W/cm².The resistance decreases by 98%when the temperature increases from 100?to 300°C.Secondly,after doping Zn²⁺the electron mobility of WSe₂film increased about 1.4 times that of the undoped film.The photo current is about 4 times higher than the dark current;and the resistance decreases by 80%with the temperature increases.Finally,after codoped with Er³⁺and Zn²⁺the electron mobility of the WSe₂film enhanced about 3 times than that of the undoped film.At the same time co-doped film has the highest photo sensitivity,the photocurrent is increased by almost 8 times;and the resistance drops by 72%when the temperature rises.The results shows that the doping does not change the crystal structure of the film but improves the deposition rate and crystallinity of the film,and significantly enhances the photoelectric properties of WSe₂film.More,it is more sensitive to light radiation and temperature.3.The optical and electrical properties of WSe₂/Mo Se₂heterojunction are studied.It is found that the WSe₂/Mo Se₂heterojunction has good rectification characteristics when there is no light illumination.The current increased from 0.08?A in the dark state to 7.36?A at 405 nm,16 m W/cm²light irradiation,increased about 90 times.The heterojunction is also extremely sensitive to the wavelength of light irradiation.At the same time,the resistance increased from 1.5×10⁵?to 1.2×10⁷?under different wavelengths of light from 405 to 655 nm,increased 2 orders of magnitude.Moreover,the junction resistance changes transiently from 5.1×10⁷?(dark)to 1.3×10⁵?(light)under 405 nm,20 m W/cm²,100 s periodic illumination.It shows that the heterojunction has an extremely short relaxation process,steep switching characteristics and good repeatability,and exhibits good light response characteristics.