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Two-dimensional (2D) semiconducting materials have proved to be very promising for the development of various electronic devices, including wearables and smaller electronics. These materials can have significant advantages over their bulky counterparts, for instance retaining their carrier mobility irrespective of their reduced thickness.

Despite their promise for creating thin electronics, 2D semiconductors have so far only rarely been used to create monolayer transistors, thinner versions of the crucial electronic components used to modulate and amplify electrical current inside most existing devices. Most proposed monolayer transistors based on 2D semiconductors were created using a few carefully selected materials known to have relatively stable lattice structures, such as graphene, tungsten diselenide or molybdenum disulfide (MoS2).

Researchers at Hunan University, the Chinese Academy of Sciences and Wuhan University recently set out to develop new monolayer transistors using alternative 2D semiconducting materials that have so far been primarily used to create multi-layer transistors, including black phosphorus (BP) and germanium arsenide (GeAs). Their work is published in the journal Nature Electronics.

"For a number of promising 2D materials—such as black phosphorus and germanium arsenide—the fabrication of monolayer transistors is challenging and is limited by the difficulties in forming robust electrical contacts with the delicate 2D materials," Wangying Li, Quanyang Tao and their colleagues wrote in their paper. "We report the fabrication of monolayer black phosphorus and germanium arsenide transistors with three-dimensional raised contacts using a van der Waals peeling technique."

The primary objective of the recent work by this team of researchers was to create new transistors based on monolayer 2D semiconductors beyond those that have so far been primarily used in monolayer transistor designs. This presents several challenges, as some of these materials are difficult to scale down uniformly and without compromising their intrinsic properties.