Phosphorene, an elemental 2D material, which is the monolayer of black phosphorus, has been mechanically exfoliated recently. In its bulk form, black phosphorus shows high carrier mobility (~10000 cm 2 /V· s) and a ~0.3 eV direct bandgap. Well-behaved p-type field-effect transistors with mobilities of up to 1000 cm 2 /V· s, as well as phototransistors, have been demonstrated on few-layer black phosphorus, showing its promise for electronics and optoelectronics applications due to its high hole mobility and thickness-dependence direct bandgap. However, p-n junctions, the basic building blocks of modern electronic and optoelectronic devices, have not yet been realized based on black phosphorus. In this paper, we demonstrate a gate tunable p-n diode based on a p-type black phosphorus/n-type monolayer MoS2 van der Waals p-n heterojunction. Upon illumination, these ultra-thin p-n diodes show a maximum photodetection responsivity of 418 mA/W at the wavelength of 633 nm, and photovoltaic energy conversion with an external quantum efficiency of 0.3%. These p-n diodes show promise for broadband photodetection and solar energy harvesting.Key words: black phosphorus, phosphorene, MoS2, p-n diode, van der Waals heterojunction, photodetection, solar cell 3 The successful isolation of graphene from graphite has led to its extensive study in physics, materials, and nano-engineering due to its extraordinary electrical and mechanical properties. [1][2][3][4] However, a lack of a bandgap limits its potential for electronic device applications, and has inspired the exploration of other 2D layered materials. [5][6][7] Among them, transition metal dichalcogenides (TMDCs), such as MoS2, are the most studied materials. [8][9][10][11] Recently, phosphorene, the monolayer form of black phosphorus, has been successfully isolated. 12 Analogous to graphite and graphene, black phosphorus is a stack of phosphorene monolayers, bound together by van der Waals interactions. 12,13 Bulk black phosphorus shows a ~0.3 eV direct bandgap and a mobility of up to ~10000 cm 2 /V· s. 14-17 Its bandgap increases as its thickness decreases, and is predicted to have a >1 eV direct bandgap in its monolayer form. 12,13 Well-behaved p-type field-effect transistors with mobilities of up to 1000 cm 2 /V· s, as well as inverters, have been demonstrated on few-layer black phosphorus. 12,13,[18][19][20] Based on its direct bandgap, few-layer black phosphorus phototransistors have been demonstrated with a responsivity of 4.8 mA/W. 19 These results indicate that black phosphorus is a promising candidate for both high performance electronics and optoelectronics applications due to its ultra-thin 2D nature, high hole mobility, and narrower direct bandgap compared to most of TMDCs. P-N junctions are the basic building blocks of modern semiconductor devices, including diodes, bipolar transistors, photodiodes, light-emitting diodes, and solar cells. In the conventional p-n homo-junction, the p-and n-type regions are formed by 4 chemically doping a bulk semiconduct...

The so-called Boltzmann tyranny defines the fundamental thermionic limit of the subthreshold slope of a metal-oxide-semiconductor field-effect transistor (MOSFET) at 60 mV dec at room temperature and therefore precludes lowering of the supply voltage and overall power consumption . Adding a ferroelectric negative capacitor to the gate stack of a MOSFET may offer a promising solution to bypassing this fundamental barrier . Meanwhile, two-dimensional semiconductors such as atomically thin transition-metal dichalcogenides, due to their low dielectric constant and ease of integration into a junctionless transistor topology, offer enhanced electrostatic control of the channel . Here, we combine these two advantages and demonstrate a molybdenum disulfide (MoS) two-dimensional steep-slope transistor with a ferroelectric hafnium zirconium oxide layer in the gate dielectric stack. This device exhibits excellent performance in both on and off states, with a maximum drain current of 510 μA μm and a sub-thermionic subthreshold slope, and is essentially hysteresis-free. Negative differential resistance was observed at room temperature in the MoS negative-capacitance FETs as the result of negative capacitance due to the negative drain-induced barrier lowering. A high on-current-induced self-heating effect was also observed and studied.

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The metal contacts on 2D black phosphorus field-effect transistor and photodetectors are studied. The metal work functions can significantly impact the Schottky barrier at the metal-semiconductor contact in black phosphorus devices. Higher metal work functions lead to larger output hole currents in p-type transistors, while ambipolar characteristics can be observed with lower work function metals. Photodetectors with record high photoresponsivity (223 mA/W) are demonstrated on black phosphorus through contact-engineering.

In this paper, we report the observation of random telegraph noise (RTN) in highly scaled InGaAs gate-allaround (GAA) MOSFETs fabricated by a top-down approach. RTN and low-frequency noise were systematically studied for devices with various gate dielectrics, channel lengths, and nanowire diameters. Mobility fluctuation is identified to be the source of 1/f noise. The 1/f noise was found to decrease as the channel length scaled down from 80 to 20 nm comparing with classical theory, indicating the near-ballistic transport in highly scaled InGaAs GAA MOSFET. Low-frequency noise in ballistic transistors is discussed theoretically.Index Terms-Ballistic transport, gate-all-around (GAA), InGaAs, low-frequency noise, MOSFET, random telegraph noise (RTN).

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