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Black phosphorus (BP) offers unique opportunities for mid‐infrared (MIR) waveguide photodetectors due to its narrow direct bandgap and layered lattice structure. Further miniaturization of the photodetector will improve operation speed, signal‐to‐noise ratio, and internal quantum efficiency. However, it is challenging to maintain high responsivities in miniaturized BP waveguide photodetectors because of reduced light–matter interaction lengths. To address this issue, a method utilizing the slow light effect in photonic crystal waveguides (PhCWGs) is proposed and experimentally demonstrated. A shared‐BP photonic system is proposed and utilized to fairly and precisely characterize the slow light enhancement. Close to the band edge around 3.8 µm, the responsivity is enhanced by more than tenfold in the BP photodetector on a 10 µm long PhCWG as compared with the counterpart on a subwavelength grating waveguide. At a 0.5 V bias, the BP PhCWG photodetector achieves a 11.31 A W−1 responsivity and a 0.012 nW Hz−1/2 noise equivalent power. The trap‐induced photoconductive gain is validated as both the dominant photoresponse mechanism and the major limiting factor of the response speed. The BP slow light waveguide photodetector is envisioned to realize miniaturized high‐performance on‐chip MIR systems for widespread applications including environmental monitoring, industrial process control, and medical diagnostics. [ABSTRACT FROM AUTHOR]

Two-dimensional black phosphorus (BP) holds great promise for future nanoscale field-effect transistors owing to its finite bandgap and expected high carrier mobility. Nevertheless, while most studies have reported unipolar p-type or ambipolar BP transistors with a hole conduction dominance, excellent n-type transport in BP has been a critical challenge. Here, we report unipolar n-type BP transistors realized by a MgO capping layer via atomic layer deposition. By coverage with 20-nm-thick MgO, remarkable electron conduction is obtained in transistors fabricated on BP flakes of thicknesses from 2.6 to 7.6 nm, accompanied by fully suppressed hole transport. Furthermore, the unipolar electron transport is found to retain (or even improve) after a period of six months, with the highest extrinsic electron mobility reaching 135.9 cm2/Vs. The effective approach to realizing unipolar n-FETs of BP demonstrated in this letter paves the way to the implementation of BP-based CMOS digital logic circuits. [ABSTRACT FROM AUTHOR]

Abstract: Achieving excellent electrostatic control and immunity to short channel effects are the formidable challenges in ultrascaled devices. 3D device architectures, such as nanoribbon, have successfully mitigated these problems by achieving uniform top‐ and side‐wall control of the channel. Here, by leveraging on the merits of 3D structure, high‐mobility black phosphorus nanoribbon field‐effect transistors (BPNR‐FET) are demonstrated and the anisotropic transport properties are systematically investigated. A simple top‐down reactive ion etching method is used to realize both armchair‐ and zigzag‐oriented nanoribbons with various widths down to 60 nm. The mobility of BPNR‐FET is found to be width‐ and thickness‐dependent, with the highest hole mobility of ≈862 cm2 V−1 s−1 demonstrated in armchair‐oriented device at room temperature by combining high‐κ gate dielectric and hydrogen treatment to reduce sidewall scattering. Furthermore, hydrogenation effectively passivates the nanoribbon dangling bonds, leading to hysteresis and contact resistance improvement. This work unravels the superior electrical performance underscore a conceptually new device based on BP nanoribbons, paving the way toward the development of nonplanar devices on 2D materials platform. [ABSTRACT FROM AUTHOR]

Abstract: Recently, both lateral and vertical p–n junctions have been realized in 2D materials using various strategies, with a number of works on exploring the potential of lateral heterojunctions resulting from thickness‐modulated bandgaps at the interface. Here, electrically tunable all‐black‐phosphorus (BP) lateral heterojunction diodes, without the need of split‐gating or selective chemical doping or transfer‐based vertical stacking, are experimentally demonstrated. The BP heterojunction diode, which exhibits an ultralow off‐state current density of 8 pA µm−1 at a mere Vd of 100 mV and a significant gate‐tunable current‐rectifying behavior with the highest rectification ratio exceeding 600, is able to harvest solar energy at both visible and near‐infrared wavelengths beyond the bandgap limitation of transition metal dichalcogenides. Specifically, at 660 nm, the device achieves an open‐circuit voltage (Voc) of 210 mV and a short‐circuit current (Isc) of 1.5 nA at 3.6 W cm−2 power density, resulting in an external quantum efficiency of 7.4% which outperforms both split‐gating and chemically doped homojunctions. This work paves the way for the exploitation of BP lateral heterojunction for broadband energy harvesting towards future optoelectronic applications. [ABSTRACT FROM AUTHOR]

2D layered materials based p-n junctions are fundamental building block for enabling new functional device applications with high efficiency. However, due to the lack of controllable doping technique, state-of-the-art 2D p-n junctions are predominantly made of van der Waals heterostructures or electrostatic gated junctions. Here, the authors report the demonstration of a spatially controlled aluminum doping technique that enables a p-n homojunction diode to be realized within a single 2D black phosphorus nanosheet for high performance photovoltaic application. The diode achieves a near-unity ideality factor of 1.001 along with an on/off ratio of ≈5.6 × 103 at a low bias of 2 V, allowing for low-power dynamic current rectification without signal decay or overshoot. When operated under a photovoltaic regime, the diode's dark current can be significantly suppressed. The presence of a built-in electric field additionally gives rise to temporal short-circuit current and open-circuit voltage under zero external bias, indicative of its enriched functionalities for self-powered photovoltaic and high signal-to-noise photodetection applications. [ABSTRACT FROM AUTHOR]

The rediscovery of graphene in the recent past has propelled the rapid development of exfoliation and other thin layer processing techniques, leading to a renewed interest in black phosphorus (BP). Since 2014, BP has been extensively studied due to its superior electronic, photonic, and mechanical properties. In addition, the unique intrinsic anisotropic characteristics resulting from its puckered structure can be utilized for designing new functional devices. In retrospect, significant efforts have been directed toward the synthesis, basic understanding, and applications of BP in the fields of nanoelectronics, ultrafast optics, nanophotonics, and optoelectronics. Here, the recent development of BP‐based devices, such as nanoribbon field‐effect transistors, complementary logic circuits, memory devices, and the progress made in meeting the challenges associated with contact resistance, in‐plane anisotropy, and advanced gate stack, are reviewed. Finally, the prospects of 2D materials in meeting the International Technology Roadmap for Semiconductor requirements for the year 2030 are discussed. The recent development of black phosphorus based electronic devices, such as nanoribbon field‐effect transistors, complementary logic circuits, memory, and the progress made in meeting the challenges associated with contact resistance, in‐plane anisotropy, and advanced gate stack are reviewed. The prospects of 2D materials in meeting the International Technology Roadmap for Semiconductor requirements for the year 2030 are also discussed. [ABSTRACT FROM AUTHOR]