2D semiconducting materials have immense potential for future electronics due to their atomically thin nature, which enables better scalability. While the channel scalability of 2D materials has been extensively studied, the current understanding of contact scaling in 2D devices is inconsistent and oversimplified. Here physically scaled contacts and asymmetrical contact measurements (ACMs) are combined to investigate the contact scaling behavior in 2D field-effect transistors. The ACMs directly compare electron injection at different contact lengths while using the exact same MoS2 channel, eliminating channel-to-channel variations. The results show that scaled source contacts can limit the drain current, whereas scaled drain contacts do not. Compared to devices with long contact lengths, devices with short contact lengths (scaled contacts) exhibit larger variations, 15% lower drain currents at high drain-source voltages, and a higher chance of early saturation and negative differential resistance. Quantum transport simulations reveal that the transfer length of Ni-MoS2 contacts can be as short as 5 nm. Furthermore, it is clearly identified that the actual transfer length depends on the quality of the metal-2D interface. The ACMs demonstrated here will enable further understanding of contact scaling behavior at various interfaces.
Keywords: contact scaling; current crowding; negative differential resistance; transfer length; two-dimensional field-effect transistors.
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