Abstract
In two-dimensional (2D)-semiconductor-based field-effect transistors and optoelectronic devices, metal–semiconductor junctions are one of the crucial factors determining device performance. The Fermi-level (FL) pinning effect, which commonly caused by interfacial gap states, severely limits the tunability of junction characteristics, including barrier height and contact resistance. A tunneling contact scheme has been suggested to address the FL pinning issue in metal–2D-semiconductor junctions, whereas the experimental realization is still elusive. Here, we show that an oxidized-monolayer-enabled tunneling barrier can realize a pronounced FL depinning in indium selenide (InSe) transistors, exhibiting a large pinning factor of 0.5 and a highly modulated Schottky barrier height. The FL depinning can be attributed to the suppression of metal- and disorder-induced gap states as a result of the high-quality tunneling contacts. Structural characterizations indicate uniform and atomically thin-surface oxidation layer inherent from nature of van der Waals materials and atomically sharp oxide–2D-semiconductor interfaces. Moreover, by effectively lowering the Schottky barrier height, we achieve an electron mobility of 2160 cm2/Vs and a contact barrier of 65 meV in two-terminal InSe transistors. The realization of strong FL depinning in high-mobility InSe transistors with the oxidized-monolayer presents a viable strategy to exploit layered semiconductors in contact engineering for advanced electronics and optoelectronics.
Highlights
We address the FL pinning effect in 2Dsemiconductor-based transistors by demonstrating highperformance indium selenide (InSe) field-effect transistors with an atomically thin, precisely controlled tunneling barrier made by a surface oxidation layer (OL)
The InSe samples are mechanically exfoliated from InSe crystals onto a highly doped Si substrate with a 300 nm SiO2 dielectric layer under ambient conditions
The OL is uniformly grown, and the underlying InSe layers remain of a high-quality crystallinity, highlighting an atomically sharp and clean interface
Summary
Two-dimensional (2D) semiconductors present great potential for electronics and optoelectronics applications due to several unique characteristics, including efficient electrostatics, a lack of shortchannel effects, and the absence of dangling bonds.[1,2,3,4,5,6] Recent studies revealed that one of the challenges of fabricating 2Dsemiconductor-based transistors is to achieve an Ohmic contact at the interface of the electrodes and the 2D semiconductors.[7,8,9,10,11] In conventional bulk semiconducting devices, the Ohmic contact can be realized by matching the work function of the metals to the bands of the semiconductors.[12,13,14] Kim et al.[15] have shown a strong Fermi-level (FL) pinning in 2D-semiconductor transistors; i.e., the Schottky barrier height (SBH), ΦSB, is virtually independent of the work function of contact metals, resulting in a lack of tunability of contact resistance as well as the low-fieldeffect mobility and output current.[6]. Compared with the InSe sample without the OML, the InSe devices embedded with the OML exhibit a higher Ids and lower barrier height (Supplementary Fig. S7), which is consistent with the tunneling contact behavior.[20]
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