Observing the semiconducting band-gap alignment of MoS2 layers of different atomic thicknesses using a MoS2/SiO2/Si heterojunction tunnel diode

Abstract

We demonstrate a tunnel diode composed of a vertical MoS 2 /SiO 2 /Si heterostructure. A MoS 2 flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS 2 layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS 2 layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4927529] Downsizing of Si field-effect transistors (FETs) has allowed ever-advancing performance and integration of electrical circuits. The downsizing also provides Si with unique characteristics including band-gap opening, 1,2 energy-level quantization, 3,4 and valley splitting, 5,6 which open ways for fascinating applications, e.g., a resonant tunneling diodes, 3 a light emitting diodes, 6,7 and a tool for tunneling spectroscopy. 4 In particular, tunneling spectroscopy, which is typically done using a scanning tunneling microscopy (STM), provides not only information about energy quantization, not observable in conventional current characteristics of FETs, but also can be used to implement light emitting devices. 8 These approaches promise for "More than Moore," which expands functions of Si FETs and their circuits. However, since Si has indirect band gap and heavy electron mass, applications utilizing band-diagram engineering have limitations compared to compound semiconductors. Two-dimensional materials, on the other hand, have recently emerged as a candidate to substitute Si in "Beyond CMOS." With direct bandgaps and lighter electron masses, two-dimensional materials have attracted much attention because of their potential for electronic and optical applications as well as physics. The research on the twodimensional materials had been boosted by the pioneering works on graphene 9,10 and has covered other materials including transition-metal dichalcogenides MX 2 and black phosphorous. 11-13 These two-dimensional materials are composed of layers with strong in-plane bonds and with weak van der Waals force mediated interlayer interactions, making possible to exfoliate them into atomically thin layers. MoS 2 , one of the layered MX 2 materials, has been studied widely for various applications such as transistors, 14,15 photo sensors, 16,17 and valleytronics and spintronics devices. 18,19 In analogy with other two-dimensional materials, the band gap of MoS 2 is modulated by the number of MoS 2 layers, showing an indirect band gap of 1.28 eV in bulk that increases while reducing the number of layers. In the single-layer limit, MoS 2 exhibits a direct band gap of 1.9 eV, 20,21 promising for light-emitting diodes. 22,23 In any applications using two-dimensional ma...

First principles calculations of the interface properties of a-Al2O3/MoS2 and effects of biaxial strain

“…[31][32][33] Low dimensional materials are interesting not only because they can provide access to novel physical phenomena, but also because their unique electrical, optical and mechanical properties make them the focus of attention. [34][35][36][37][38] MoS 2 crystal is composed of Mo atomic layer sandwiched between two layers of S, forming a triangular prismatic arrangement. 39,40 The Mo-S bonding is strong covalent, but the coupling between MoS 2 monolayer is weak van der Waals interactions.…”

First principles calculations of the interface properties of amorphous-Al2O3/MoS2 under non-strain and biaxial strain conditions

“…In the following, we discuss the VBO and CBO at a-Al 2 O 3 /MoS 2 interface in Fig. 04 37 The VBO and CBO based on GGA-PBE calculations are 0.48 eV and 1.55 eV for 1-layer MoS 2 , 0.89 eV and 1.59 eV for 2-layer MoS 2 , 0.88 eV and 1.71 eV for 3-layer MoS 2 , 0.91 eV and 1.68 eV for 4-layer MoS 2 , and 1.00 eV and 1.69 eV for bulk MoS 2 . GGA-PBE underestimates the band gap, which leads to inaccurate VBO and CBO.…”

The highly-efficient light-emitting diodes based on transition metal dichalcogenides: from architecture to performance

“…The tunneling diode (p–i–n) composed of a vertical MoS 2 /SiO 2 /Si heterostructure was also demonstrated. 58 The ionic-liquid gated light-emitting transistor was fabricated on WS 2 monolayer and bilayers. 59 For TMDCs, the p–n junction can be divided into two kinds: the first one is the vertical p–n junction, which shows large EL intensity for large junction area; the second one is the lateral p–n junction, which shows weaker EL intensity for relatively smaller junction area.…”