Tunable contact resistance in transition metal dichalcogenide lateral heterojunctions

Abstract

Contact resistance of semiconducting transition metal dichalcogenides has been shown to decrease in lateral heterojunctions formed with their metallic phases but its origins remain elusive.Here we combine first principles and quantum transport calculations to rationalize the contact resistance of these structures in terms of phase, composition (WTe 2 , MoTe 2 , WSe 2 , and MoSe 2 ), and length of the channel. We find that charge injection in metallic 1T'-WTe 2 /1T'-MoTe 2 junctions is nearly ideal as electrode Bloch states remain delocalized through the channel. Mixtures of 1T' selenides and tellurides depart from this scenario due to the momentum mismatch between states in the lead and channel. In semiconducting channels, the large Schottky barriers degrade the electrical contacts. Around band edges, contact resistance values are about an order of magnitude lower than those obtained experimentally suggesting that doping and phase-engineering could be employed to overcome this issue. We predict that transport regime in these junctions shifts from thermionic emission to tunneling for channels shorter than 3 nm at room temperature. We also discuss the presence of states at the metal/semiconductor interfaces. By underpinning mechanisms to control the contact resistance in heterogeneous two-dimensional materials, this work proves valuable towards the development of devices suitable for optoelectronics and phase-change materials applications.1 Atomically thin crystals [1] have become unique platforms to novel physical phenomena unseen in the bulk [2]. These two-dimensional (2D) materials -such as graphene, hexagonal boron nitride, transition metal chalcogenides, and phosphorene among others -have attracted great attention due to their diverse electrical, mechanical, thermal, and optical properties [3][4][5][6][7][8]. Within this growing class of materials, much interest in the pursuit of nanoscale device applications has been given to the group VI transition metal dichalcogenides (TMDs) with the stoichiometric formula MX 2 , where M is Mo or W, and X is a member of the chalcogen family (S, Se or Te) [9]. Group VI TMDs are mostly semiconducting with band gaps of up to 1.9 eV [10] making them potential candidates for ultrathin, flexible low-power electronics and valleytronics [11,12]. In addition, a special feature of this