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Observation of tunable band gap and anisotropic Dirac semimetal state in black phosphorus

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Science  14 Aug 2015:
Vol. 349, Issue 6249, pp. 723-726
DOI: 10.1126/science.aaa6486

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Tuning the band gap of black phosphorus

Most materials used in electronics are semiconductors. The sizable energy gap in their electronic structure makes it easy to turn the conduction of electricity on and off. Graphene naturally lacks this band gap unless it undergoes certain modifications. Kim et al. studied the electronic structure of black phosphorus—a related two-dimensional material. By sprinkling potassium atoms on top of single layers of black phosphorus, the material changed from being a semiconductor to having a gapless linear dispersion similar to that of graphene.

Science, this issue p. 723

Abstract

Black phosphorus consists of stacked layers of phosphorene, a two-dimensional semiconductor with promising device characteristics. We report the realization of a widely tunable band gap in few-layer black phosphorus doped with potassium using an in situ surface doping technique. Through band structure measurements and calculations, we demonstrate that a vertical electric field from dopants modulates the band gap, owing to the giant Stark effect, and tunes the material from a moderate-gap semiconductor to a band-inverted semimetal. At the critical field of this band inversion, the material becomes a Dirac semimetal with anisotropic dispersion, linear in armchair and quadratic in zigzag directions. The tunable band structure of black phosphorus may allow great flexibility in design and optimization of electronic and optoelectronic devices.

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