| Two-dimensional layered transition metal chalcogenides（TMDCs）with atomically thickness,rich energy band properties,good carrier transport characteristics and excellent optical properties are considered as one of promising candidates for novel electronic and optoelectronic devices.It is very important to modulation the transport properties of TMDCs and their heterostructures for high-performance and multifunctional electronic and optoelectronic devices.In this thesis,we mainly studied the modulation of electrical and opto-electrical properties of TMDCs and their heterostructures by back-gate modulation and N2O plasma doping,and realized high-performance and tunable electronic/optoelectronic devices such as field-effect transistors（FETs）,photodetectors and tunneling field-effect transistors.The main contents are as follows:1.The modulation of electronic and optoelectronic properties of TMDCs and their heterostructures by gate voltage is investigated.Firstly,we studied the modulation of Fermi levels of Mo Te2 and BP（or WTe2）by gate voltage and found that they behaved differently under the gate modulation.On the basis,we utilized the gate to modulation the band alignments of the Mo Te2/BP and Mo Te2/WTe2 van der Waals heterojunctions,so that the value and direction of the Fermi level difference between Mo Te2 and BP（or WTe2）were changed,thereby realized tunable Mo Te2/BP and Mo Te2/WTe2 van der Waals heterojunctions with reversible rectification characteristics and positive and negative optical responses.2.The regulation of N2O plasma doping technology on the performances of TMDCs was studied.We developed the N2O plasma doping process and realized the controllable and non-volatile doping of TMDCs semiconductor devices including WSe2,Mo Se2,WS2,Mo Te2 and Mo S2.The research was mainly focus on the modulation and mechanism of N2O plasma on the electrical and optoelectronic performances of WSe2.After doping,the WSe2 FET realized high hole mobility and carrier concentration and low contact resistance.Besides,the doped WSe2 photodetector exhibited high photoresponse(1.5×105 A W-1),high gain（106）and fast response（40 ms）under visible light.3.We studied the modulation of TMDCs van der Waals heterojunctions by N2O plasma.Firstly,the electrical performances of Mo Te2 and Mo S2 FETs were investigated after N2O plasma doping.It is found that the N2O plasma had opposite p-type and n-type doping effects on Mo Te2 and Mo S2,respectively,which could adjust the concentration of holes and electrons effectively.Then,we revealed the mechanism of opposite doping effects on Mo Te2 and Mo S2 using X-ray photoelectron spectroscopy,Raman spectroscopy,Kelvin probe force microscopy and nano-cutting technology.Finally,the Mo Te2/Mo S2 van der Waals heterojunction realized a p-n diode with a high rectification ratio and a tunneling transistor with high peak-to-valley current ratio under different doping levels. |
