Fast and Broadband Photoresponse of Few-Layer Black
Phosphorus Field-Effect Transistors
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Abstract
Few-layer black phosphorus, a new
elemental two-dimensional (2D)
material recently isolated by mechanical exfoliation, is a high-mobility
layered semiconductor with a direct bandgap that is predicted to strongly
depend on the number of layers, from 0.35 eV (bulk) to 2.0 eV (single
layer). Therefore, black phosphorus is an appealing candidate for
tunable photodetection from the visible to the infrared part of the
spectrum. We study the photoresponse of field-effect transistors (FETs)
made of few-layer black phosphorus (3–8 nm thick), as a function
of excitation wavelength, power, and frequency. In the dark state,
the black phosphorus FETs can be tuned both in hole and electron doping
regimes allowing for ambipolar operation. We measure mobilities in
the order of 100 cm<sup>2</sup>/V s and a current ON/OFF ratio larger
than 10<sup>3</sup>. Upon illumination, the black phosphorus transistors
show a response to excitation wavelengths from the visible region
up to 940 nm and a rise time of about 1 ms, demonstrating broadband
and fast detection. The responsivity reaches 4.8 mA/W, and it could
be drastically enhanced by engineering a detector based on a PN junction.
The ambipolar behavior coupled to the fast and broadband photodetection
make few-layer black phosphorus a promising 2D material for photodetection
across the visible and near-infrared part of the electromagnetic spectrum