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Atomically Thin Device Exhibits Tunable Electrical Behavior

22 October 2013

Northwestern University researchers have integrated two atomically thin materials—molybdenum disulfide and carbon nanotubes—to create a p-n heterojunction diode, among the most ubiquitous components of modern electronics.

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.

“We anticipate that this work will enable new types of electronic functionality and could be applied to the growing number of emerging two-dimensional materials,” said Mark Hersam, director of the Northwestern University Materials Research Center.

Over the past decade, researchers have been isolating atomically thin two-dimensional crystals, such as graphene, a single-atom-thick carbon lattice. While significant progress has been made to stack two or more distinct two-dimensional materials to create high-performance, ultrathin electronic devices, one of the most important electronic components, a p-n heterojunction diode derived from ultrathin materials, is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits.

Northwestern University researchers have demonstrated 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 percent and fast photoresponse of less than 15 microseconds—good enough for use in diverse ultrathin, high-performance electronics and in optoelectronics.

The researchers have also demonstrated and fabricated an atomic layer ultrafast photodetector with an electronically tunable wavelength response.

The research, “Gate-Tunable Carbon Nanotube-MoS2 Heterojunction p-n Diode,” was published October 21 in the Proceedings of the National Academy of Sciences.

The National Science Foundation-funded Materials Research Science and Engineering Center (MRSEC) and the Office of Naval Research funded the research.

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