Fabrication And Electrical Characteristics Of WSe₂ And MoS₂ Transistors With H-BN Encapsulation

Two-dimensional(2D)transition metal dichalcogenides,such as molybdenum disulfide and tungsten diselenide,hold merits of high switching ratio and sizable carrier mobility for applications as field-effect-transistors.They have emerged as attractive candidates of transistor channels for post-silicon microelectronics,owing to the concurrence of structural properties of perfect flatness and atomic thickness.However,2D materials are very sensitive to external environment and hence their surface is prone to be effected by extrinsic carrier scattering sources,resulting in considerable degradation in device performance.Therefore,it is highly desired to seek a convenient and controllable strategy for preserving the intrinsic electrical transport of 2D semiconductors,in order to improve the overall device performance.The main results of this thesis are as follows.First,we realized a method for the integration of patterned electrodes and effective surface passivation for 2D materials.The method relies on the transfer and re-stacking strategy developed for van der Waals force materials.In brief,the purposes of surface passivation and contact to patterned electrodes of 2D materials are realized by transferring the top h-BN/2D material stacks onto underlying h-BN substrates with predefined metal electrodes.Second,h-BN encapsulated MoS₂ and WSe₂ transistors were fabricated and carefully characterized by optical microscope,Raman,photoluminescence,AFM and other techniques.It was revealed that the double-sided h-BN encapsulation is effective in surface passivation,featuring advantages of clean channel interfaces free of bubbles and non-invasivity to the vulnerable atomic 2D channels.Third,the electrical transport properties of the devices were characterized with a low-temperature,high-vacuum probe station.It was found that the transistors of h-BN encapsulated bilayer WSe₂ exhibit bipolar conduction behavior,with low-temperature electron mobility of 1521cm²V^-1s^-1,a contact resistance of 57 k?·?m and a n-type Schottky barrier height of 0.5 e V.Another transistor consisted of 6-layer MoS₂ channels shows a low current hysteresis of0.38%and a subthreshold swing of 83 m V/dec at room temperature,and a low-temperature electron mobility exceeding 4200 cm²V^-1s^-1.The corresponding interfacial trap density extracted from back gating is as low as 4.1×10¹¹ cm^-2e V^-1.The results indicate that the device preparation method established here is compatible with a variety of 2D materials,and the electronic performance of the as-encapsulated devices is dramatically improved in contrast to counterparties without h-BN encapsulation.Moreover,the performance of our devices are comparable to those prepared with more complex encapsulation and electrode integration technology.In one word,our method provides a convenient solution for high performance device based on 2D materials.