Integration of two atomically thin materials – molybdenum disulfide and carbon nanotubes into nanoscale electronics

Northwestern University researchers have now taken a significant step toward fabricating complex nanoscale electronics. By integrating two atomically thin materials – molybdenum disulfide and carbon nanotubes—they have created a p-n heterojunction diode, an interface between two types of semiconducting materials.

Among the most widely used electronic structures, the p-n junction diode forms the basis of a number of technologies, including solar cells, light-emitting diodes, photodetectors, computers, and lasers.

In addition to its novel electronic functionality, the p-n heterojunction diode is also highly sensitive to light. This attribute has allowed the authors to fabricate and demonstrate an ultrafast photodetector with an electronically tunable wavelength response.

PNAS – Gate-tunable carbon nanotube–MoS2 heterojunction p-n diode

Significance

The p-n junction diode is the most ubiquitous and fundamental building block of modern electronics, with far-reaching applications including integrated circuits, detectors, photovoltaics, and lasers. With the recent discovery and study of atomically thin materials, opportunities exist for adding new functionality to the p-n junction diode. Here we demonstrate that a p-n heterojunction diode based on atomically thin MoS2 and sorted semiconducting carbon nanotubes yields unprecedented gate tunability in both its electrical and optical properties, which is not observed in the case of bulk semiconductor devices. In addition to enabling advanced electronic and optoelectronic technologies, this p-n heterojunction diode provides new insight into charge transport and separation at atomically thin heterointerfaces.

Abstract

The p-n junction diode and field-effect transistor are the two most ubiquitous building blocks of modern electronics and optoelectronics. In recent years, the emergence of reduced dimensionality materials has suggested that these components can be scaled down to atomic thicknesses. Although high-performance field-effect devices have been achieved from monolayered materials and their heterostructures, a p-n heterojunction diode derived from ultrathin materials is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits. Here we demonstrate a gate-tunable p-n heterojunction diode using semiconducting single-walled carbon nanotubes (SWCNTs) and single-layer molybdenum disulfide as p-type and n-type semiconductors, respectively. The vertical stacking of these two direct band gap semiconductors forms a heterojunction with electrical characteristics that can be tuned with an applied gate bias to achieve a wide range of charge transport behavior ranging from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104. This heterojunction diode also responds strongly to optical irradiation with an external quantum efficiency of 25% and fast photoresponse

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