Interpenetrated Graphene/WSe2 Lateral Heterostructures for Barrierless Ohmic-Contacted p-FETs

Abstract

High contact resistance between TMDs and metals has been identified as an outstanding issue. TMDs tend to form a substantial Schottky barrier (SB) with commonly used metals. Air-stable graphene electrodes stacked on the WSe 2 by transfer technique have been reported. However, unipolar conduction has not been achieved in FETs based on TMD materials and graphene electrodes. Here we report a synthetic process to directly grow WSe 2 monolayers along the edge of patterned few-layered graphene, forming the lateral heterojunction between the graphene and monolayer WSe 2 . The few-layered WSe 2 bridges the few-layer graphene and monolayer WSe 2 , and an interpenetrating layered structure is formed between graphene and WSe 2 . As a result, the WSe 2 monolayer channel and the junction to the graphene can be formed at the same time by the synthesis method, where graphene serves as source and drain. Graphene is in-situ heavily p-doped by H 2 with covent bond during WSe 2 growing process. Such a unique junction structure leads to a barrier less ohmic contact between doped graphene and WSe 2 . Unipolar WSe 2 PFET with laterally contacted p-doped graphene source/drain (p-G/WSe 2 PFET) can be achieved for the first time. With Pd contacted source/drain metal, the unipolar PFET perform Ion/Ioff > 10 5 and field effect mobility ~20 cm2/Vˑs. Moreover we can still have unipolar PFET with Ti source/drain metal exceeds 10 3 Ion/Ioff ratio even Ti work function is low (4.3 eV) and close to the conduction band edge of WSe 2 (electron affinity of WSe 2 ~ 4.03 eV).