Recently, negative differential resistance devices have attracted considerable attention due to their folded current-voltage characteristic, which presents multiple threshold voltage values. Because of this remarkable property, studies associated with the negative differential resistance devices have been explored for realizing multi-valued logic applications. Here we demonstrate a negative differential resistance device based on a phosphorene/rhenium disulfide (BP/ReS2) heterojunction that is formed by type-III broken-gap band alignment, showing high peak-to-valley current ratio values of 4.2 and 6.9 at room temperature and 180 K, respectively. Also, the carrier transport mechanism of the BP/ReS2 negative differential resistance device is investigated in detail by analysing the tunnelling and diffusion currents at various temperatures with the proposed analytic negative differential resistance device model. Finally, we demonstrate a ternary inverter as a multi-valued logic application. This study of a two-dimensional material heterojunction is a step forward toward future multi-valued logic device research.

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Phosphorene/rhenium disulfide heterojunction-based negative differential resistance device for multi-valued logic.

The mid-infrared (mid-IR) is a wavelength range with a variety of technologically vital applications in molecular sensing, security and defense, energy conservation, and potentially in free-space communication. The recent development and rapid commercialization of new coherent mid-infrared sources have spurred significant interest in the development of mid-infrared optical systems for the above applications. However, optical systems designers still do not have the extensive optical infrastructure available to them that exists at shorter wavelengths (for instance, in the visible and near-IR/telecom wavelengths). Even in the field of optoelectronic sources, which has largely driven the growing interest in the mid-infrared, the inherent limitations of state-of-the-art sources and the gaps in spectral coverage offer opportunities for the development of new classes of lasers, light emitting diodes and emitters for a range of potential applications. In this topical review, we will first present an overview of the current state-of-the-art mid-IR sources, in particular thermal emitters, which have long been utilized, and the relatively new quantumand interband-cascade lasers, as well as the applications served by these sources. Subsequently, we will discuss potential midinfrared applications and wavelength ranges which are poorly served by the current stable of mid-IR sources, with an emphasis on understanding the fundamental limitations of the current source technology. The bulk of the manuscript will then explore both past and recent developments in midinfrared source technology, including narrow bandgap quantum well lasers, type-I and type-II quantum dot materials, type-II superlattices, highly mismatched alloys, lead-salts and transitionmetal-doped II-VI materials. We will discuss both the advantages and limitations of each of the above material systems, as well as the potential new applications which they might serve. All in all, this topical review does not aim to provide a survey of the current state of the art for mid-IR sources, but instead looks primarily to provide a picture of potential next-generation optical and optoelectronic materials systems for mid-IR light generation.

https://iopscience.iop.org/article/10.1088/2040-8986/aa939b/pdf

Next-generation mid-infrared sources

Disorder‐Induced Optical Heterogeneity in Single CdSe Nanowires

Frontiers in the Growth of Complex Oxide Thin Films: Past, Present, and Future of Hybrid MBE

Fabrication of MoS2/WSe2 heterostructures as electrocatalyst for enhanced hydrogen evolution reaction

This review deals with a study of optical and magnetotransport phenomena at a type II arsenide–antimonide heterojunction with a broken-gap alignment. A fundamental feature of this structure is partial overlapping of the InAs conduction band with the GaSb-rich solid solution valence band. In such a heterostructure, electrons and holes are spatially separated and localized in self-consistent quantum wells formed on both sides of the heterointerface. This leads to unusual tunnelling-assisted radiative recombination transitions and novel transport properties. Results of a pioneering study of interface-related luminescence in type II broken-gap GaInAsSb/InAs heterostructures, with a high quality abrupt heteroboundary, grown by the LPE method, are presented. The energy band diagram of the type II broken-gap GaInAsSb/InAs(GaSb) heterostructures and band overlapping control, depending on a doping level and epilayer composition of quaternary solid solution, are discussed. A 2D-electron channel with high Hall mobility at the p-GaInAsSb/p-InAs interface was found and examined. A great deal of attention is paid to quantum transport properties of the semimetal channel in a wide magnetic field range (up to 18 T) at low temperatures. A cyclotron resonance study was used to obtain data on the energy spectrum at the interface and to estimate effective masses for subbands in the semimetal channel. The intriguing behaviour of the 2D-electron system in the presence of localized holes in high magnetic fields and the first observation of integer quantum Hall effect plateaus on the type II single GaInAsSb/InAs heterointerface formed by LPE are demonstrated. A tunnelling-injection laser with high asymmetric band offset confinements based on the type II broken-gap heterojunction is considered. Applications of the interface-induced phenomena in luminescent and transport properties for the design of novel mid-IR optoelectronic devices and Hall sensors are briefly reviewed.

https://iopscience.iop.org/article/10.1088/0268-1242/19/10/R03/pdf

Interface-induced optical and transport phenomena in type II broken-gap single heterojunctions

A mid-IR laser based on a hybrid pseudomorphic AlGaAsSb/InAs/CdMgSe heterostructure with a III–V/II–VI heterovalent interface at the 0.6-μm-InAs active region has been fabricated by molecular-beam epitaxy on p+-InAs substrate. It provides ∼1.5-eV asymmetric barriers for both electrons and holes in InAs, inhibiting carrier leakage from the active region. Despite a nonoptimal defect density at the CdMgSe/InAs interface (106–107 cm−2), the structure demonstrates lasing at ∼2.78 μm (up to 100 K) under pulse injection pumping with the threshold current density of 3–4 kA/cm2. The proposed design is promising for high-power mid-IR lasers operating at room temperature.

A 2.78-μm laser diode based on hybrid AlGaAsSb/InAs/CdMgSe double heterostructure grown by molecular-beam epitaxy

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III–V part) and CdMgSe/CdSe (as a II–VI part), has been proposed as a basic element of a midinfrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy and has exhibited an intense long-wavelength electroluminescence at 3.12 μm (300 K). A less than 10 times reduction of electroluminescence intensity from 77 to 300 K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔEC=1.28 eV and ΔEV∼1.6 eV. The type of band lineups at a coherent InAs/Cd1−xMgxSe interface is discussed for 0⩽x⩽0.15.

Room-temperature midinfrared electroluminescence from asymmetric AlSbAs/InAs/CdMgSe heterostructures grown by molecular beam epitaxy

Type II antimonide–arsenide based heterostructures have recently received great attention from researchers engaged in the design of mid-infrared optoelectronic devices. Magnetotransport properties of the semimetal channel and the interface electroluminescence were experimentally studied on type II broken-gap GaInAsSb/InAs single heterojunctions grown by LPE with high quality interface. An electron channel with high Hall mobility was, for the first time, observed at the interface of isotype p-GaInAsSb/p-InAs heterojunctions with undoped and slightly doped quaternary layers at low temperatures. A depletion of the electron channel was found to be due to the heavy acceptor doping level of the quaternary layer. The two-dimensional nature of the interface carriers was established by Shubnikov–de Haas oscillation experiments at 1.8–4.2 K under magnetic fields up to 9–14 T. Intensive interface electroluminescence in the structures under study was observed in the spectral range of 3–4 µm at low temperatures (4.2–77 K). A model of the recombination transition at the type II broken-gap interface was proposed and experimentally confirmed. A new physical approach to the design of mid-infrared tunnelling-injection lasers is demonstrated.

Konstantin D. Moiseev

Papers

Interface-induced optical and transport phenomena in type II broken-gap single heterojunctions

A 2.78-μm laser diode based on hybrid AlGaAsSb/InAs/CdMgSe double heterostructure grown by molecular-beam epitaxy

Room-temperature midinfrared electroluminescence from asymmetric AlSbAs/InAs/CdMgSe heterostructures grown by molecular beam epitaxy

Interface-induced phenomena in type II antimonide-arsenide heterostructures

Quantum dots and quantum dashes in the narrow-gap InSb/InAsSbP system