Abstract
Achieving low resistance contacts and high carrier mobility are common concerns for obtaining high performance of graphene devices. In graphene FETs (GFETs), the work functions (WF) of electrode materials and metal-graphene (M-G) contact configurations have remarkable influences on contact properties of M-G. In this work, the contact properties of Cu-G are improved prominently by inserting a nanoscale MoOx (x<3) ultra-thin layer formed by annealing Mo film in the air atmosphere at 150°C between the electrode and graphene in GFETs. Results show that MoOx can not only induce the p-doping, but also induce end contact to graphene characterized by Mo-C carbide formation from the XPS and TEM results. The relationship between the improvement of contact properties of M-G and the thickness of MoOx layer inserted at source/drain region was further investigated. It is shown that, within 0-3 nm thickness of MoOx, the thicker the MoOx deposited, the better the output characteristics and the greater the field mobilities are. The mechanism of that MoOx deposited at source-drain helps improving the carrier mobility is discussed and is related to improved interface between graphene and SiO2. This study provides a simple and important way to improve contact properties of M-G and carrier mobility of contact and graphene FET.
Highlights
Graphene is a two-dimensional (2D) nano-material composed of carbon atoms which are sp2 hybridized and fabricated in a honeycomb lattice
Many theoretical and experimental works show that MoO3 can cause p-doping in graphene and the contact resistance can decrease with first increase of MoOx thickness and would become saturate
RC of M-G was mostly measured by transfer length methods (TLM)9,10,30 The total resistance (Rtotal) between the source and drain in a graphene FETs (GFETs) is considered as the combination of the RC and the length-dependent channel resistance (RL), that is Rtotal = 2RC + RL
Summary
Graphene is a two-dimensional (2D) nano-material composed of carbon atoms which are sp hybridized and fabricated in a honeycomb lattice. To increase the DOS, graphene is heavily doped in the contact region through many measures, such as substitutional doping by N, As or B,12–14 and surface-transfer doping by using materials with different work function.. The surface-transfer method is versatile, majorly using material with different work function (WF) with graphene. Many theoretical and experimental works show that MoO3 can cause p-doping in graphene and the contact resistance can decrease with first increase of MoOx thickness and would become saturate.. Forming edge contact between metal and graphene, in which covalent bond between carbon and metal atoms forms, can achieve significantly low contact resistance.. Many effective measures have been taken to induce edge contact of graphene such as ultraviolet/ozone treatment of the graphene surface, fabricating graphene antidot arrays under metal electrode, forming cuts in graphene within the contact regions, which are achieved by promoting the reaction of metal and carbon atoms in graphene. The mechanism of contact resistance decrease due to charge transfer and end contact formation was discussed
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