Rational Control Growth Of Two-dimensional TMDs Heterostructures For High-performance Optoelectronics

Two-dimensional(2D)semiconductors,as the star materials for leading the rapid development of integrated circuit technology in the post-Moore era,have important application prospects in future fields of communication,information and optoelectronics due to their ultra-thin physical size,novel physicochemical properties and excellent optoelectronic performances.The 2D layered semiconductor materials represented by transition metal chalcogenides(TMDC)have diverse bandgap structures and differernt carrier types.In particular,the heterostructures,which consist of different TMDC semiconductor with forbidden-band widths,electron affinity,dielectric constant,and light absorption coefficients,possess not only the excellent properties of each component,but also bring an extremely rich interface characteristics.The development of TMDC heterostructures will powerfully promote the industry progress of integrated electronic device,such as transistors,flexible devices,detectors and light-emitting diodes with semiconductor heterojunctions as the core.Nowadays,mechanical transfer method is widely used in the fabrication and research of 2D heterojunctions.However,a numble of factors,including stress introduction,interface pollution,size limitation and low manufacturing efficiency seriously restricte the industrialization application in future integrated devices.Therefore,the direct preparation of ultra-thin TMDC-based heterostructures with various types,high quality and excellent performances still remains an urgent problem to be solved in the field of highly integrated electronic devices.With these ideas in mind,we taken the controllable preparation and device application of 2D TMDs semiconductor heterostrcutures as the starting point in this dissertation,and realized the universal synthesis of the 2D high quality TMDC heterostructures by designing and improving the growth strategy of traditional chemical vapor deposition.We constructed a series of new optoelectronic devices through micro-nano processing technologies,and investigated the effect of the heterojunction interface on the device performances.At the same time,based on the theoretical calculations,we have developed a synthesis method of 2D-template strain-induced method for controllable growth of the ultra-thin hexagonal-phase(h-phase)GaTe.Based on the achieved high quality GaTe/MoS₂heterostructures,high-performance photodetectors are designed and prepared.The main achievements are summarized as follows:(1)With an in-depth comprehending towards the growth mechanism of transition metal dichalcogenides(TMDCs)vertical heterostructures,through rational control of the metal/chalcogenide ratio in vapor precursors,we realized the effective manipulation of the diffusion barrier of the active-clusters on 2D-templates.The active-clusters with high diffusion barrier will induce the nucleation on top of TMDC templates to realize vertical heterostructures,while the active-clusters with low diffusion barrier will induce the nucleation on edge of TMDC templates to realize lateral heterostructures.By rational kinetics control of the nucleation sites and heteroepitaxy direction on the 2D-template,we realized the growth of systematic configurations of high quality TMDC heterostructures at low temperature.The universal growth strategy provides a robust material platform for the future application of heterogeneous junction photoelectric devices.(2)Based on the obtained high-quality bilayer MoS₂/MoSe₂vertical heterostructures,a novel optoelectronic device was designed and prepared,where two electrodes are separately fabricated on MoS₂-template and heterostructure region forming a parallel-series mode channel.The existence of the built-in electric field in heterostructure significantly improves the device performance,which helps to enhance the mobility up to 5 times and the photoresponse up to 2 orders as compared with that of monolayer MoS₂.Meanwhile,a fast response speed is observed.This work demonstrates that the introduction of heterostructure interface and the formation of the built-in electric field play a significant role in modifying the optoelectronic device properties.(3)By using improved chemical vapor deposition method and introducing two-dimensional MoS₂as the substrate,we realized the direct growth of the ultra-thin h-GaTe,leading to high quality h-GaTe/MoS₂vertcial stacked heterostructures.Theoretical calculation studies reveal that GaTe with hexagonal phase is more thermodynamically stable on MoS₂template than the monoclinic-phase GaTe,which can be attributed to the strain stretching and the formation-energy reduction.Based on the achieved ultra-thin h-GaTe/MoS₂p-n heterostructures,optoelectronic devices are designed and probed,where remarkable photoresponsivity(32.5 A/W)and fast photoresponse speed(<50?s)are obtained under zero bias voltage,indicating well-behaved photo-sensing behaviors.