Crystallized Monolayer Semiconductor for Ohmic Contact Resistance, High Intrinsic Gain, and High Current Density

• Published in: Advanced materials (Weinheim) 2020-08, Vol.32 (34), p.e2002281-n/a
• Main Authors: Peng, Boyu, Cao, Ke, Lau, Albert Ho Yuen, Chen, Ming, Lu, Yang, Chan, Paddy K. L.
• Format: Article
• Language: English
• Subjects: Contact resistance; Crystallization; Crystals; Current density; Field effect transistors; Field emission; Flexible components; Materials science; molecular crystals; Monolayers; Multilayers; Organic crystals; Saturation; semiconductors; Thermal management; Thermionic emission
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202002281

The contact resistance limits the downscaling and operating range of organic field‐effect transistors (OFETs). Access resistance through multilayers of molecules and the nonideal metal/semiconductor interface are two major bottlenecks preventing the lowering of the contact resistance. In this work, monolayer (1L) organic crystals and nondestructive electrodes are utilized to overcome the abovementioned challenges. High intrinsic mobility of 12.5 cm2 V−1 s−1 and Ohmic contact resistance of 40 Ω cm are achieved. Unlike the thermionic emission in common Schottky contacts, the carriers are predominantly injected by field emission. The 1L‐OFETs can operate linearly from VDS = −1 V to VDS as small as −0.1 mV. Thanks to the good pinch‐off behavior brought by the monolayer semiconductor, the 1L‐OFETs show high intrinsic gain at the saturation regime. At a high bias load, a maximum current density of 4.2 µA µm−1 is achieved by the only molecular layer as the active channel, with a current saturation effect being observed. In addition to the low contact resistance and high‐resolution lithography, it is suggested that the thermal management of high‐mobility OFETs will be the next major challenge in achieving high‐speed densely integrated flexible electronics. Contact resistance and intrinsic gain are important performance indicators of organic field‐effect transistors. Staggered‐structure devices based on highly crystallized monolayer organic semiconductor provide outstanding contact, carrier mobility, and intrinsic gain. Organic 2D materials can potentially play an important role in next‐generation flexible electronics.