Graphene Oxide as a Promising Hole Injection Layer for MoS₂-Based Electronic Devices

M any two-dimensional (2D)materials exist in bulk form as stacks of bonded layers with weak van der Waals interlayer attraction. Thanks to their particular structure, they can be exfoliated into atomically thin monolayers that hold promise for next-generation flexible electronics and optoelectronics. Graphene has received much attention in the past decade, due in large part to exceptional electronic properties such as its ultrahigh carrier mobility. However, the absence of a band gap has limited the progress of graphene-based technologies. For example, graphene field-effect transistors (FETs) cannot be turned off effectively, and even though small bandgapshave been successfully opened in graphene, 7 the development of devices operating at room temperaturewith a low stand-bypower dissipation remains a challenge. On the other hand, transition-metal dichalcogenides (TMDCs) are a class of directband gap semiconductors that are emerging as strong candidates in next-generation nanoelectronic devices. 12 In the monolayer form, their lack of dangling bonds, structural stability, and mobility values comparable to Si make them optimal as channel materials in FETs. In particular, FETs based on single layerMoS2, which has a direct band gap of 1.8 eV and mobility in the range 1 50cmV 1 s 1 at room temperature, 17 show low power dissipation, efficient control over switching and reduction of shortchannel effects. However, in order to develop logic circuits based on TMDCs, it is necessary to fabricate both nand p-type FETs. TMDC FETs based on a Schottky device architecture can transport either electrons (n-FET) or holes (p-FET) in the conducting channel, depending on whether the Schottky barrier height (SBH) is smaller relative to the conduction or the valence band, respectively. While monolayer n-FETs have been widely reported, fabrication of p-FETs has been challenging. This is due to the relative difficulty in designing MoS2/metal contacts * Address correspondence to [email protected].