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Black phosphorus field-effect transistors

Why this mattered

Black phosphorus field-effect transistors mattered because they showed that the post-graphene search for two-dimensional electronics did not have to choose between graphene’s high mobility and transition-metal dichalcogenides’ usable bandgaps. Li and colleagues demonstrated few-layer black phosphorus devices operating at room temperature, including sub-7.5 nm channels with current modulation around (10^5), clear current saturation, and field-effect mobility reported near 205 cm² V⁻¹ s⁻¹ for 5 nm samples. That combination made black phosphorus one of the first compelling examples of a thin, layered semiconductor that could plausibly support logic-device behavior rather than only high-conductance transport.

The paradigm shift was not simply that another 2D material had been exfoliated, but that black phosphorus introduced a qualitatively different design space: an elemental, layered semiconductor with a thickness-dependent direct bandgap, relatively high carrier mobility, and strong in-plane anisotropy. After this paper, “phosphorene” became a serious platform for nanoelectronics and optoelectronics, motivating work on ambipolar transport, photodetectors, p-n junctions, van der Waals heterostructures, strain-tunable devices, and encapsulation strategies to manage environmental instability. Its later impact was therefore twofold: it expanded the catalog of viable 2D semiconductors beyond graphene and MoS₂-like compounds, and it sharpened the central materials lesson of the field: useful 2D electronics would depend on balancing bandgap, mobility, contacts, stability, and thickness control, not on any single headline property.

Abstract

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