'Etch-a-sketch' technique fabricates 2D semiconductor

July 31, 2020 //By Rich Pell
'Etch-a-sketch' technique fabricates 2D semiconductor
Researchers at New York University (NYU) Tandon school of Engineering say they have demonstrated nanofabrication of "p-n junctions" - a basic electronic building block - on a single atomic layer.

While one-atom-thick 2D materials offer great potential in the electronics industry, say the researchers, a major obstacle for their wide application is the unsolved challenge of the scalable and robust nanofabrication of the elemental electronic building block for semiconductors - the p–n junction . In their work, the researchers demonstrated a novel approach based on thermal scanning probe lithography (t-SPL) to fabricate state-of-the-art "p-n junctions" on a single atomic layer of molybdeunum disulfide (MoS 2) - a transition metal dichalcogenide .

To produce p-n junctions, it is necessary to dope a semiconductor in such a way that part of it is n-doped (doped with an excess number of negatively-charged electrons) and another part is p-doped (doped with an excess number of positively-charged "holes"). The researchers showed that by combining t-SPL with defects nanoengineering it was possible to obtain nanoscale-resolution bipolar doping of MoS 2, yielding to both n-type and p-type conduction, which can be readily extended to other 2D semiconductors.

As part of their work, the researchers integrated t-SPL - using a probe heated above 200 degrees Celsius - with a flow-through reactive gas cell to achieve a unique nanoscale control of the local thermal activation of defects in monolayer MoS 2. The defective patterns can give rise to either p- or n-type conductivity on demand, depending on the gases used during the local heating process.

Doping and defects formation mechanisms, say the researchers, are elucidated at the molecular level by means of X-ray photoelectron spectroscopy, transmission electron microscopy, and density functional theory.

“In our previous research we showed that t-SPL outperforms electron beam lithography and other standard methods for fabricating metal electrodes on MoS 2," says Elisa Riedo, professor at the New York University (NYU) Tandon school of Engineering, "an advance that could also decrease the cost of fabrication since t-SPL does not require markers or vacuum."

With this consecutive success in bipolar doping of

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