This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A transistor normally requires several fundamentally different materials—a semiconductor to carry current, an insulating dielectric to control it and metallic contacts through which current enters and leaves. Integrating all of these components becomes increasingly difficult as semiconductor devices approach the atomic scale.
A research team led by Director Jo Moon-Ho of the Center for Van der Waals Quantum Solids within the Institute for Basic Science (IBS) has now demonstrated a fundamentally different approach. Instead of fabricating the semiconductor, dielectric and contact materials separately and then assembling them into a device, the researchers started from a single layered crystal and chemically converted selected atomic layers and regions into the different materials needed for a working transistor. The work is published in the journal Science.
Atomically thin two-dimensional semiconductors have long been considered promising candidates for future electronics as conventional silicon devices approach their physical scaling limits. Yet despite more than two decades of research, one of the greatest obstacles to practical 2D electronics has not been the performance of the semiconductor itself, but the difficulty of integrating it with other components. A transistor requires a highly uniform gate dielectric as well as low-resistance electrical contacts, but the surfaces of 2D semiconductors contain few sites where other materials can readily attach.
This makes it difficult to deposit conventional dielectric materials uniformly. Direct deposition of metals can also damage the atomically thin semiconductor or create large contact barriers that reduce device performance. Mechanical transfer methods, in which separate 2D materials are peeled, positioned and stacked one by one, have provided an alternative, but such processes are difficult to scale uniformly over large areas and remain poorly suited to mass production.
The IBS team instead used the crystal itself as the starting material for all of the required electronic functions. The researchers began with multilayer tungsten diselenide (WSe₂), a 2D semiconductor. Its electrical properties can be changed by replacing some of the atoms surrounding the tungsten layer.
By preserving the tungsten framework while selectively replacing these surrounding atoms, the researchers were able to change the electronic character of individual regions without rebuilding the entire crystal. The upper layers of WSe₂ were first oxidized into insulating tungsten oxide (WOₓ). The oxide could then be further converted through vapor-phase reactions into tungsten disulfide (WS₂), an n-type semiconductor, or tungsten ditelluride (WTe₂), a semimetal.
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