High-Mobility Holes in Dual-Gated WSe₂ Field-Effect Transistors

Abstract

We demonstrate dual-gated p-type field-effect transistors (FETs) based on few-layer tungsten diselenide (WSe2) using high work-function platinum source/drain contacts and a hexagonal boron nitride top-gate dielectric. A device topology with contacts underneath the WSe2 results in p-FETs with ION/IOFF ratios exceeding 10(7) and contacts that remain ohmic down to cryogenic temperatures. The output characteristics show current saturation and gate tunable negative differential resistance. The devices show intrinsic hole mobilities around 140 cm(2)/(V s) at room temperature and approaching 4000 cm(2)/(V s) at 2 K. Temperature-dependent transport measurements show a metal-insulator transition, with an insulating phase at low densities and a metallic phase at high densities. The mobility shows a strong temperature dependence consistent with phonon scattering, and saturates at low temperatures, possibly limited by Coulomb scattering or defects.

The ambipolar transport behavior of WSe2 transistors and its analogue circuits

“…Coulomb scattering originating from the interfacial charged impurity is one of the key scattering mechanisms. Although the interfacial charged impurity can be screened by introducing high-k dielectric, ion-gel, and BN 23,27,36,38 , the complex fabrication and higher cost need to be taken into consideration. Interestingly, the hole branch in the 1L WSe 2 transistor disappears, suggesting that the effect of interfacial charged impurities on the hole carrier is much stronger than that on the electron carrier, while the interfacial charged impurity is screened in the 7L WSe 2 transistor and leads to a similar effect on hole mobility and electron mobility.…”

“…More significantly, different from the unipolar n-type semiconductor MoS 2 with the presence of sulfur vacancy and the strong Fermi level pinning near the conduction band [19][20][21] , WSe 2 as an ambipolar semiconductor has been demonstrated as having Fermi level effectively shifting between the valence band and the conduction band under application of an external field [22][23][24] . Recently, the optical and hole dominant transport properties of exfoliated WSe 2 have been explored [24][25][26][27] . To facilitate the potential application of WSe 2 in CMOS, it is essential to understand the underlying ambipolar hole and electron transport mechanisms.…”

Density-Dependent Quantum Hall States and Zeeman Splitting in Monolayer and Bilayer WSe2

“…Recent advances in sample fabrication have now facilitated more detailed studies of the electron physics in TMDs [9][10][11]. Tungsten diselenide (WSe 2 ) is of particular interest because of a large spin-orbit splitting in the valence band [12], high-mobility [10], and low temperature Ohmic contacts [13].In this work, we report on the magnetotransport of holes in mono-and bilayer WSe 2 in the quantum Hall regime. An examination of the Shubnikov-de Haas (SdH) oscillations, and the quantum Hall states (QHSs) sequence reveals interesting carrier density-dependent transitions between predominantly even and predominantly odd filling factors (FFs) as the hole density is tuned.…”

“…1(b) the optical micrograph of an hBN encapsulated WSe 2 sample with bottom Pt contacts, and separate local top-and back-gates. The mono-and bilayer WSe 2 Hall bar samples were fabricated using a modified van der Waals assembly technique [13,14]. The bottom Pt electrodes in combination with a large, negative topgate bias (V T G ) ensure Ohmic hole contacts to the WSe 2 [10,13].…”

“…Recent advances in sample fabrication have now facilitated more detailed studies of the electron physics in TMDs [9][10][11]. Tungsten diselenide (WSe 2 ) is of particular interest because of a large spin-orbit splitting in the valence band [12], high-mobility [10], and low temperature Ohmic contacts [13].…”