Controllable Growth Of Single-layer And Few-layer Tungsten Selenide Films And Their Optoelectronics Properties

Transition metal chalcogenides?TMDs?,an important class of two-dimensional?2D?materials,is receiving wide attention in the field of materials science due to its many unique properties,such as optical transparency,high carrier mobility,and widely adjustable band gap.Among the different TMDs,WSe2,an air-stable material,is of particular interest because it is one of the few known 2D pure phase layered p-type semiconductors.WSe2 has been demonstrated to be an ideal material for building next generation of electronic and optoelectronic devices,with great application prospects in field effect transistors,photodetectors,gas sensors,piezoelectric sensors and photovoltaic solar cells.Therefore,the realization of WSe2 synthesis with large area,high quality and controllable layers is of great significance and is the foundation of relavent applied research.This thesis focus on the systematic research into WSe2,including controllable synthesis of WSe₂ with different size and thickness,as well as its characterization,electronic device performance and optoelectronic device performance.?1?Using Se pellets as selenium source,WO₃ powder as tungsten source,Si/SiO₂?300nm?as growth substrate,and Ar/H₂ mixture as carrier gas,WSe₂ single crystals with different thickness as well as mono-and double-layered WSe₂ continuous large films were prepared by chemical vapor deposition.The results show that different growth parameters have great influence on the morphology,size and layer-number of the resulting WSe₂.By adjusting the experimental parameters,mono-layer to five-layer WSe2 can be obtained with the maximum sizes reaching 500?m,320?m,280?m,200?m and 150?m respectively,and the band gap transitions from the direct band gap of 1.62 eV to the indirect band gap of 1.53 eV.The fluorescence aging phenomenon of WSe₂ was studied by fluorescence microscope.?2?The electrical and photoelectric detection properties of the multilayer WSe₂ are studied.The results show that the resistance decreases and the mobility increases with the increase of the number of layers.WSe₂ also exhibits different types of semiconductor characteristics with increasing layer number,mono-to five-layer WSe₂ are p-type,n-type,bipolar,n-type,n-type,respectively.By comparing the photodetection performance of mono-to five-layer WSe₂ phototransistors,it is found that five-layer WSe₂phototransistors have the best photodetection performance.The optical response rate,optical detection rate and external quantum efficiency are 47.5 A/W,1.08×10¹22 Jones and1.08×104%,respectively.By adjusting the gate voltage,the optical response rate of the five-layer WSe₂ photodetector can reach 2.62×10⁴ A/W.