Black Phosphorus Mid-Infrared Photodetectors with High Gain

Abstract

Recently, black phosphorus (BP) has joined the two-dimensional material family as a promising candidate for photonic applications due to its moderate bandgap, high carrier mobility, and compatibility with a diverse range of substrates. Photodetectors are probably the most explored BP photonic devices, however, their unique potential compared with other layered materials in the mid-infrared wavelength range has not been revealed. Here, we demonstrate BP mid-infrared detectors at 3.39 μm with high internal gain, resulting in an external responsivity of 82 A/W. Noise measurements show that such BP photodetectors are capable of sensing mid-infrared light in the picowatt range. Moreover, the high photoresponse remains effective at kilohertz modulation frequencies, because of the fast carrier dynamics arising from BP's moderate bandgap. The high photoresponse at mid-infrared wavelengths and the large dynamic bandwidth, together with its unique polarization dependent response induced by low crystalline symmetry, can be coalesced to promise photonic applications such as chip-scale mid-infrared sensing and imaging at low light levels.

Protective molecular passivation of black phosphorus

“…7 Its thickness-dependent direct bandgap varies in the range of 0.3-2.0 eV (from single-layer to bulk, respectively), making BP suitable to optoelectronics in a broad spectral range. [8][9][10] With high room-temperature mobility, exceeding 1000 cm 2 V −1 s −1 in thin films, BP is also a very promising material for electronics. However, BP is sensitive to oxygen and humidity 11 due to its threefold coordinated atoms.…”

Photogating in Low Dimensional Photodetectors

“…So far, the equation G = τ/τ T (τ is the excess minority carrier lifetime, τ T is the carrier transit time) is widely used to estimate the optical gain in photogating enhanced photodetectors 29, 31, 39. Photogating can be regarded as a particular example of photoconductive effect, because both have the same expression of gain and need to work at a bias voltage.…”

Midinfrared Electro-optic Modulation in Few-Layer Black Phosphorus

“…All of these make BP a very promising material for broadband, hyperspectral optoelectronic applications. Indeed, many types of photodetectors based on black phosphorus have been demonstrated, operating in the visible and the near-IR bands [10][11][12]25,26 . These photodetectors show high responsivity and low dark current-thanks to BP's bandgap, which is a significant advantage over graphene-and very high response speed 12 .…”

“…While mid-IR laser sources have become commercially available 33 and integrated photonic circuits have been developed on the ubiquitous silicon-on-insulator platform 31,34 , mid-IR photodetection still relies on narrowband compound semiconductors such as InAsSb and HgCdTe, which are difficult to be integrated with silicon. As an alternative, BP mid-IR photodetectors have already been demonstrated with promising performance 25,26 . For mid-IR optical modulation, multilayer BP is equally promising 35 .…”