Dielectric and Gate Metal Engineering for Threshold Voltage Modulation in Enhancement Mode Monolayer MoS ₂ Field Effect Transistors

Abstract

ABSTRACT Excellent gate electrostatics in field effect transistors (FETs) based on 2D transition metal dichalcogenide (2D TMD) channels can dramatically decrease static power dissipation. Energy‐efficient FETs operate in enhancement mode with a small and positive threshold voltage (V th ) for n‐type devices. However, most state‐of‐the‐art FETs based on monolayer MoS 2 channel operate in depletion mode with negative V th due to doping from the underlying dielectric substrate. In this work, we identify key properties of the semiconductor/dielectric interface (MoS 2 on industrially relevant high dielectric constant ( k ) HfO 2 , ZrO 2 and hBN for reference) responsible for realizing enhancement‐mode operation of 2D MoS 2 channel FETs. We find that hBN and ZrO 2 dielectric substrates provide low defect interfaces with MoS 2 that enables effective modulation of the V th using gate metals of different work functions (WFs). We use photoluminescence (PL) and synchrotron X‐ray photoelectron spectroscopy (XPS) measurements to investigate doping levels in monolayer MoS 2 on different dielectrics with different WF gate metals. We complement the FET and spectroscopic measurements with capacitance‐voltage analysis on dielectrics with varying thicknesses, which confirms that V th modulation in ZrO 2 devices is correlated with WF of the gate metals – in contrast with HfO 2 devices that exhibit signatures of V th pinning induced by oxide/interface defect states. Finally, we demonstrate FETs using a 2D MoS 2 channel and a 6 nm of ZrO 2 dielectric, achieving a subthreshold swing of 87 mV dec −1 and a threshold voltage of 0.1 V. Our results offer insights into the role of dielectric/semiconductor interface in 2D MoS 2 based FETs for realizing enhancement mode FETs and highlight the potential of ZrO 2 as a scalable high‐ k dielectric.