High Number of Transport Modes: A Requirement for Contact Resistance Reduction to Atomically Thin Semiconductors

Electrical contacts to atomically thin 2-D semiconductors are considered as the hindering aspect of electronic devices based on these materials. The high resistance of such contacts stems from their Schottky nature in contrast to the desired low-resistance Ohmic contacts. This issue of Schottky contacts is thus one of the major inhibitors to the integration of 2-D materials into mainstream technology. In this work, we explore contact resistance ( RC ) to atomically thin 2-D semiconductors in terms of the injected current through the Schottky barrier (SB) by using the Landauer-Büttiker formalism as well as experimental measurements and technology computer aided design (TCAD) simulations. We show that the SB height and width, which are determined by the metal-semiconductor interface and the number of charge carriers in the semiconductor channel, respectively, affect RC when it is relatively high ( RC > 1 kΩ μ m ). However, the number of transport modes for carrier injection is the limiting factor for aggressive RC lowering ( RC < 1 kΩ μ m ), even for near-zero SB height. Our results show that to reduce RC below 100 Ω μ m , large number of transport modes are required, which can be accomplished through raising the number of channel carriers above 5. 1013 cm-2 by means of heavy doping or gating. Our conclusions offer insight for future contact engineering and can explain recently published state-of-the-art results.