Archive | 2019
Optical and Optoelectronic Properties of Black Phosphorus and Recent Photonic and Optoelectronic Applications
Abstract
DOI: 10.1002/smtd.201900165 mobility and are indirect semiconductors in their few-layer forms.[5] The III–VI layered materials, such as GaSe and InSe, have direct bandgap even down to few layers and show broadband photoresponse from ultraviolet (UV) to near-infrared (NIR).[12–18] While in the short-wavelength infrared (SWIR) and mid-infrared (MIR) range, BP shows its unique properties and merits as a promising semiconductor for photodetection. Indeed, one distinct advantage of BP, from the prospective of the semiconductor industry, is the direct bandgap which varies from ≈0.3 eV in the bulk to ≈2.0 eV in monolayer, which bridges the “electromagnetic spectrum gap” between graphene and TMDs.[19] The direct bandgap preserved from bulk to monolayer facilitates light–matter interactions. In addition, the direct and moderate bandgap of BP is readily tunable by varying the layer number,[20] strain engineering,[21] chemical tailoring,[22] vertical electric field tuning,[23,24] and so on. The flexible bandgap modulation is expected to spur versatile photonic and optoelectronic applications of BP such as photodetectors and electro-optic modulators with broadband photoresponse spanning the visible and MIR regions.[11,25–27] Another beneficial feature of BP is the relatively ideal tradeoff in the current on–off ratio for carrier mobility. Zhang and co-workers and Ye and co-workers have characterized the electrical transport properties of BP with a nanoscale thickness (≈10 nm).[28,29] The mobility of BP-based field effect transistors (FETs) is as high as ≈1000 cm2 V−1 s−1 (at room temperature). Although it cannot compare with that of graphene-based FETs, BP outperforms TMDs and even commercial siliconbased devices.[30] The current on–off ratio of BP (≈103–105) is four orders of magnitude higher than that of graphene, although it is still several orders of magnitude lower than that of TMDs (≈108–1010).[30] Therefore, from the perspective of FET performance and by considering the two crucial parameters of mobility and on–off ratio, BP bridges the gap between graphene and TMDs. Remarkably, BP FETs exhibit the ambipolar behavior without special treatments which are needed in TMDs.[31–33] This switching behavior between n-type and p-type by gate control renders BP a promising semiconductor in logic devices and photovoltaic applications.[34–36] BP has strong in-plane anisotropy, similar to other anisotropic layered materials such as WTe2, ReSe2, and SnSe.[37] The prominent anisotropy in BP stems from the puckered lattice structure which becomes even more remarkable with reduced dimensionality.[38] This in-plane anisotropy of 2D BP The rapid development of the semiconductor industry calls for the exploration of novel semiconductors to cater to modern technical and commercial needs. Recently, black phosphorus (BP) has emerged as a new class of 2D semiconducting material and has attracted intensive research attention. The high carrier mobility and tunable direct bandgap of BP deliver great promise in photonic and optoelectronic device applications. Furthermore, the unique intrinsic anisotropy arising from the puckered structure can be exploited in the design of new devices. This review briefly introduces the history of BP and puts emphasis on recent advances pertaining to its optical properties and applications in the photonic and optoelectronic fields. From the perspective of mass production and practical use of BP, some of the research challenges and opportunities are discussed. Black Phosphorus