Infrared optical anisotropic properties and photocarriers lifetime in 2D black phosphorus by angle-resolved absorption and reflectometry

Abstract

In this article, angle and polarization-resolved absorption and time-resolved pump-probe measurements have been carried out on multilayer black phosphorus (BP) at infrared wavelength (around 1550 nm), which is an extension of the previous studies of the BP behavior done at higher frequency [Lazar et al., Nanoscale 10(19), 8979–8988 (2018)]. Exfoliated down to a few layers, BP reveals the properties of a 2D material with anisotropic response, high mobility (up to 10 000 cm2/V/s), and absorption, which are very relevant to optoelectronics. BP bandgap is tunable according to the number of layers, allowing applications from UV to IR. The bandgap height of the single and thicker layers has been measured through absorption and reflection spectra. We report the measurement of the ambipolar carrier lifetime, which has been determined to be about 15 ps. The structure-induced anisotropy is studied. The results confirm BP as a suitable material for ultrafast devices such as microwave photoswitches, samplers, terahertz antenna, for instance.