Optimizing Performances Of MoTe₂-based Nanodevices With Controllable Doping

The development of silicon-based electronics is approaching its predicted scaling limit of⁵ nm due to short channel effects.The emergence of graphene has leads to a research boom in new two-dimensional?2D?layered materials.Because of atomically uniform thickness,absence of surface dangling bonds,high mobility and low current leakage,2D layered materials have been exhibiting the potential of becoming next generation nanoelectronics for replacing silicon,which also provide the new direction for the continuation of the Moore's Law.Graphene has ultrahigh mobility and transconductance characteristics,so it is applied to achieve radio frequency analog transistors with a cutoff frequency of hundreds of gigahertz.However,graphene channel can't be switched into‘off state'because it has no bandgap,which greatly limits its applications in field-effect transistors?FETs?of digital logic circuits.Recently,novel class of 2D layered materials,transition metal dichalcogenides?TMDCs?,have a bandgap of¹.0-2.0 eV with the certain dependence on the thickness.Therefore,FETs based on 2D TMDCs exhibit high on/off ratio,low subthreshold swing?SS?,high mobility and low current leakage characteristics.However,TMDCs FETs usually present p-,n-,or ambipolar transport behavior.Basic logic devices such as diodes and logic inverters all rely on different p-n-type transport characteristics on a same semiconductor.But most current modification methods to tune carrier properties of 2D semiconductor materials are complicated and high-cost.Here,we provide two simple and controllable modification methods in this work.The first method is air annealing at low temperature of 150 ^oC,inducing the continuous and effect modulation of carrier polarity from n-to p-type.The hole mobility is significantly improved from 0.1 to 28 cm² V^-11 s^-1,indicating a strongly hole transport behavior.Based on this feature,we fabricated the MoTe₂ complementary inverter with a high gain of up to 108,which is highest value among all inverters based on MoTe₂.In addition,the treatment broadens the absorption spectrum towards long wavelength direction,indicating the badgap of MoTe₂ is narrowed.The second method is partial laser beam scanning in air by taking advantages of the laser?532 nm?and piezoelectric table in confocal Raman system?WITec alpha300R?.This controllable local method can also achieve continuous p-doping effect on multilayer MoTe₂and decrease SS of FET based on SiO₂ dielectric from 34 to 1.1 V/dec.The SS was improved nearly 30 times,while the electron mobility keep rising gradually,which indicates the controllable local doping is an effective means to improve characteristics of electronics.Based on the local p-doping feature,we successfully fabricated the MoTe₂ complementary inverter with an ultrahigh gain of up to 242,which is the highest value among all research reports about inverters.Besides that,we changed the conditions of laser beam scanning to make a single MoTe₂ FET generate the obvious negative transconductance?NTC?.By making use of the characteristic,the functional circuit with frequency doubling characteristic was well designed and prepared.In the study,we report two simple and easily implemented means for continuously tuning the properties of MoTe₂,in which the laser beam scanning is more controllable.We can realize the high-performance FETs,frequency doublers based on single MoTe₂ FETs and ultrahigh-gain inverters with based on a single MoTe₂ flake.Therefore,our research paves the way for the development of integrated circuits with simplifier and higher integration densities.