Nature of carrier injection in metal/2D-semiconductor interface and its implications for the limits of contact resistance

Abstract

Monolayers of transition metal dichalcogenides (TMDCs) exhibit excellent electronic and optical properties. However, the performance of these two-dimensional (2D) devices are often limited by the large resistance offered by the metal contact interface. Till date, the carrier injection mechanism from metal to 2D TMDC layers remains unclear, with widely varying reports of Schottky barrier height (SBH) and contact resistance ( ), particularly in the monolayer limit. In this work, we use a combination of theory and experiments in Au and Ni contacted monolayer MoS2 device to conclude the following points: (i) the carriers are injected at the source contact through a cascade of two potential barriers -the barrier heights being determined by the degree of interaction between the metal and the TMDC layer; (ii) the conventional Richardson equation becomes invalid due to the multi-dimensional nature of the injection barriers, and using Bardeen-Tersoff theory, we derive the appropriate form of the Richardson equation that describes such composite barrier; (iii) we propose a novel transfer length method (TLM) based SBH extraction methodology, to reliably extract SBH by eliminating any confounding effect of temperature dependent channel resistance variation; (iv) we derive the Landauer limit of the contact resistance achievable in such devices. A comparison of the limits with the experimentally achieved contact resistance reveals plenty of room for technological improvements.

High Responsivity and Photovoltaic Effect Based on Vertical Transport in Multilayer α‐In2Se3

“…Such current crowding occurs when the physical contact length becomes smaller than the transfer length ( L t ). Generally, for 2D materials (e.g., MoS 2 ), L t < 100 nm and hence the active area is much smaller than L t . In vertical devices, the current crowding mechanism is not dominating because the photogenerated carriers are swept toward the bottom electrode efficiently.…”

Gate-Tunable WSe2/SnSe2 Backward Diode with Ultrahigh-Reverse Rectification Ratio

“…spectroscopy to obtain first-hand information about charge transport processes across the interface 44 . To have an easy optical access to the photoactive WSe2 layer, for the PL experiment,…”

“…We also demonstrate an efficient modulation of the rectification ratio by tuning the applied gate voltage, contact metals, and thickness of the WSe2 layer. Finally, we show that the effective current transfer length at the heterointerface of these vertical heterojunctions can be very large encompassing the entire overlap area of WSe2 and SnSe2, avoiding current crowding, which is in sharp contrast to typical metal-2D semiconductor contact interfaces, with small transfer length 44,45 .…”

Asymmetrically Encapsulated Vertical ITO/MoS2/Cu2O Photodetector with Ultrahigh Sensitivity

“…We have further checked that removing the Cu 2 O layer (i.e., ITO/MoS 2 /Au stack) increases the dark current significantly, while almost entirely suppressing the photocurrent. This is due to large metal induced doping of MoS 2 providing negligible barrier for the electrons.…”

“…The conduction band edge of multilayer MoS 2 originates from Q valley (along Γ point to K point) with g v = 6, while the valence band edge is at the Γ point with g v = 1. Since larger valley degeneracy reduces contact resistance, electrons see a less resistance path than holes.…”