Study On Near-infrared WSe₂ Heterojunction Photodetectors

Thanks to their strong light-matter interactions,the transitional metal di-chalcogenides（TMD）films,which have earned significant interest in various optoelectronic applications,exhibit high absorption efficiency and photoelectric conversion ability,even if the thickness is on the order of nanometers.Among them,WSe₂is very suitable to construct heterostructure with narrow band-gap semiconductors,such as Si and GaAs,showing great promise in photoelectric device,benefit from its p-type electrical transport characteristics,high mobility and bandgap of 1.3-1.65 eV.Herein,we successfully prepared large area uniform WSe₂ film by selenidation of the W film deposited with magnetron sputtering equipments.The thickness of WSe₂ film can be controlled by the deposition time of W film.And photodetectors of WSe₂/Si and WSe₂/GaAs were fabricated with thin film transfer technique.The results showed that the detection wavelength range of WSe2/Si heterojunction photodetector can be adjusted by controlling the thickness of WSe2 film.With the increase of WSe2 film thickness,the response of the device to UV and visible light is effectively suppressed,and the response to near-infrared light is dominant.In addition,theoretical analysis indicates that the detection wavelength range is mainly tuned by the controllable junction region.When the WSe2 film thickness is 130 nm,at zero bias,the peak response of the device is 970 nm with FWHM of 210 nm.Meanwhile its responsivity is 0.46 A/W,and on-off ratio is up to 9.2×10⁴.It is also found that a near-infrared image system based on the WSe2/Si heterojunction photodetector showed high noise immunity to the visible and UV light.Moreover,WSe₂/GaAs showed a peak response at 810 nm with on-off ration of 16.6×10⁴ without external power supply.The two photodetectors,made of all inorganic material,exhibited high stability with response speed under milliseconds.The preparation method of the device is simple and feasible.And the results in this thesis lay a solid foundation for the application of WSe₂ in the field of high-performance optoelectronic devices.