二硒化鎢金屬化末端接觸場效電晶體與電子元件應用

對於使用僅僅只有原子層厚度的過渡金屬硫族化物(Transition-metal dichalcogenides, TMDs)作為通道材料場效電晶體(Field-effect transistors, FETs)，金屬與半導體接觸工程一直是一個很重要的議題。傳統的金屬與TMDs接觸是利用微影製程的方式形成一個上端鍵結接觸(Top-bonded contact)的結構，會夾帶一個很大的蕭特基能障。為了要提供一個對載子注入更有效的方式，在論文中提出了末端鍵結接觸(End-bonded contact)的結構，能夠使通道材料的邊緣與接觸金屬有更強的共價鍵，利用預先鍍好的WO3-x/Pd/WO3-x晶種層(Seeding layer)與化學氣相沉積(Chemical vapor deposition, CVD)的方式來形成金屬-WSe2-金屬的末端接觸結構。如此一來單層的WSe2場效電晶體表現出卓越的特性，電流密度達到30 μA/μm、電動遷移率為90 cm2/V·s、次臨限擺幅為94 mV/dec，勝過同一通道材料的上接觸結構。另一方面也使用了密度泛函理論(Density function theory, DFT)對兩者結構進行模擬計算，結果指出末端接觸的Pd-W有更強的軌域混成以及富裕的禁帶能態，對於元件形成更佳的電性表現。

關鍵字

過渡金屬硫族化物；場效電晶體；末端接觸；上接觸

並列摘要

Contact engineering has been the central issue in the context of high-performance field-effect transistors (FETs) made of atomic thin transition metal dichalcogenides (TMDs). Conventional metal contacts on TMDs have been made on top via a lithography process, forming a top-bonded contact scheme with an appreciable contact barrier. To provide a more efficient pathway for charge injection, an end-bonded contact scheme has been proposed, in which covalent bonds are formed between the contact metal and channel edges. Yet, little efforts have been made to realize this contact configuration. Here, we bridge this gap and demonstrate end-contact WSe2 by means of chemical vapor deposition, in which the channel is grown from the two opposing WO3-x/Pd/WO3-x nucleation seeds, forming metal-WSe2-metal end contacts. Monolayer WSe2 FETs thus made exhibit remarkable performance metrics, including the on-current density of 30 μA/μm, hole mobility of 90 cm2/V·s, and subthreshold swing of 94 mV/dec, surpassing those of FETs sharing with the same channel but contacted on top. Calculations using density functional theory indicates that the superior device performance stems mainly from the stronger Pd-W hybridization and substantial gap states in the end contact configuration.