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 WSe2 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 WSe2 monolayers along the edge of patterned few-layered graphene, forming the lateral heterojunction between the graphene and monolayer WSe2. The few-layered WSe2 bridges the few-layer graphene and monolayer WSe2, and an interpenetrating layered structure is formed between graphene and WSe2. As a result, the WSe2 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 H2 with covent bond during WSe2 growing process. Such a unique junction structure leads to a barrier less ohmic contact between doped graphene and WSe2. Unipolar WSe2 PFET with laterally contacted p-doped graphene source/drain (p-G/WSe2 PFET) can be achieved for the first time. With Pd contacted source/drain metal, the unipolar PFET perform Ion/Ioff > 105 and field effect mobility ~20 cm2/Vˑs. Moreover we can still have unipolar PFET with Ti source/drain metal exceeds 103 Ion/Ioff ratio even Ti work function is low (4.3 eV) and close to the conduction band edge of WSe2 (electron affinity of WSe2~ 4.03 eV).