Electric Field In Heterostructures Research Articles

Boost solar-to-hydrogen efficiency by constructing heterostructures with the pristine and Se/Te-doped AgInP2S6 monolayers

To achieve high solar-to-hydrogen efficiency (η'STH), we identify the geometrical structures of seven heterostructures comprising the pristine and doped AgInP2S6 monolayers and confirm the stabilities. The electronic properties by HSE06 with dipole corrections are used to demonstrate the charge polarization and the built-in electric field in heterostructure. The direct Z-schemes for hydrogen evolution on the heterostructures are constructed based on the projected band edge potentials of each monolayer, and the corresponding s are evaluated. The results demonstrate that both doping and constructing heterostructure can significantly boost the s. Remarkably, the Se-doped AgInP2S6 monolayer promotes the from 6.41% to 12.50%, while the two configurations of the AgInP2S3Se3/AgInP2S3Te3 heterostructure raise to 17.59% and 19.88%, respectively. The corresponding total energy conversion efficiency reach 0.37% and 0.43%. Moreover, strain engineering significantly impacts with either boosting or degrading effects depending on the different strains. The highestof 31.17% can be achieved for the AgInP2S3Se3/AgInP2S3Te3 heterostructure under 4% biaxial tensile strain. The changes of −0.15–1.69 eV for the Gibbs free energies in the hydrogen evolution reactions indicate these reactions are feasible in thermodynamics. Therefore, the heterostructures based on the Se/Te doped AgInP2S6 monolayers, especially the AgInP2S3Se3/AgInP2S3Te3 one, are a potential candidate for developing high efficient photocatalysts.

A Systematic Exploration of InGaN/GaN Quantum Well-Based Light Emitting Diodes on Semipolar Orientations -=SUP=-*-=/SUP=-

Light-emitting diodes (LEDs) based on group III-nitride semiconductors (GaN, AlN, and InN) are crucial elements for solid-state lighting and visible light communication applications. The most widely used growth plane for group III-nitride LEDs is the polar plane (c-plane), which is characterized by the presence of a polarization-induced internal electric field in heterostructures. It is possible to address long-standing problems in group III-nitride LEDs, by using semipolar and nonpolar orientations of GaN. In addition to the reduction in the polarization-induced internal electric field, semipolar orientations potentially offer the possibility of higher indium incorporation, which is necessary for the emission of light in the visible range. This is the preferred growth orientation for green/yellow LEDs and lasers. The important properties such as high output power, narrow emission linewidth, robust temperature dependence, large optical polarization ratio, and low-efficiency droop are demonstrated with semipolar LEDs. To harness the advantages of semipolar orientations, comprehensive studies are required. This review presents the recent progress on the development of semipolar InGaN/GaN quantum well LEDs. Semipolar InGaN LED structures on bulk GaN substrates, sapphire substrates, free-standing GaN templates, and on Silicon substrates are discussed including the bright prospects of group III-nitrides. Keywords: Group III-nitride semiconductor, semipolar, light-emitting diodes, InGaN/GaN quantum well.

BCN‐Assisted Built‐In Electric Field in Heterostructure: An Innovative Path for Broadening the Voltage Window of Aqueous Supercapacitor

AbstractThe relatively low operating voltage window is the main factor limiting the energy density of aqueous energy storage devices. The delicate design of heterostructured electrode materials can efficiently increase the intrinsic electrochemical performance through synergistic effects. For the first time, to broaden the voltage window of aqueous supercapacitors the synergistic effect between boroncarbonitrides (BCN) and built‐in electric field existing in heterostructures is designed to utilize. Based on this design concept, MnO/MnS@BCN electrode materials are synthesized, in which the synergistic effect can effectively strengthen the storage of electrolyte ions on the electrode surface, thus inhibiting the electrolysis of H2O and eventually broadening the voltage window of aqueous supercapacitor. In MnO/MnS@BCN‐based symmetrical supercapacitors, the voltage window of the device is extended from 1.2 V (single‐component) to 2 V, with the energy density enhanced to 75.0 W h kg−1. The strategy blazes an efficient and convenient path to broaden the intrinsic voltage window of transition metal oxide supercapacitors.

Enhanced interfacial electronic transfer of BiVO4 coupled with 2D g‐C3N4 for visible‐light photocatalytic performance

AbstractA BiVO4/2D g‐C3N4 direct dual semiconductor photocatalytic system has been fabricated via electrostatic self‐assembly method of BiVO4 microparticle and g‐C3N4 nanosheet. According to experimental measurements and first‐principle calculations, the formation of built‐in electric field and the opposite band bending around the interface region in BiVO4/2D g‐C3N4 as well as the intimate contact between BiVO4 and 2D g‐C3N4 will lead to high separation efficiency of charge carriers. More importantly, the intensity of bulid‐in electric field is greatly enhanced due to the ultrathin nanosheet structure of 2D g‐C3N4. As a result, BiVO4/2D g‐C3N4 exhibits excellent photocatalytic performance with the 93.0% Rhodamine B (RhB) removal after 40 min visible light irradiation, and the photocatalytic reaction rate is about 22.7 and 10.3 times as high as that of BiVO4 and 2D g‐C3N4, respectively. In addition, BiVO4/2D g‐C3N4 also displays enhanced photocatalytic performance in the degradation of tetracycline (TC). It is expected that this work may provide insights into the understanding the significant role of built‐in electric field in heterostructure and fabricating highly efficient direct dual semiconductor systems.

Photocatalytic conversion of CO to fuels with water by B-doped graphene/g-C3N4 heterostructure

Photocatalytic reduction of carbon monoxide (CO) is a promising route to the production of high-value chemicals and fuels, as a supplement to high energy-input Fischer-Tropsch synthesis (FTS) and a key step in direct photo/electro-reduction CO2 to multi-carbon products. However, many current research efforts for high-efficiency FTS/CO2 reduction mainly focus on the metal-based catalysts, while metal-free and solar-driven photocatalysts are rarely explored. Here, by means of Lewis acid sites, a metal-free composite photocatalyst for CO reduction, namely boron (B) doped-graphene/g-C3N4 heterostructure, is proposed. First-principles calculations show that the dopants (B) as catalytic sites can effectively capture and activate CO molecules and reduce CO to CH3OH and CH4 in different doping content. It is worth noting that C2 products, i.e., C2H5OH, can be produced with low free energy barriers on para-doped graphene/g-C3N4. Meanwhile, the competitive hydrogen evolution reaction (HER) can be greatly suppressed, leading to the high selectivity of CO reduction. Moreover, the formation of a built-in electric field in heterostructure enhances the separation of photogenerated electrons and holes, which further accelerates the transmission of photogenerated electrons to the catalytic sites and improves the reaction efficiency. Overall, this work not only proposes a new strategy from a new perspective to solve problems of high energy consumption and low selectivity of FTS, but also provides a tandem strategy to solve problems of CO2 to multi-carbon products.

Recent Developments in Semipolar InGaN Laser Diodes

Group III-nitride semiconductors (GaN, AlN, and InN) are attractive materials for a wide range of electronic and photonic applications. The most widely employed growth plane for III-nitrides is the polar plane, characterized by the presence of a polarization-induced internal electric field in heterostructures. To eliminate the deleterious effects of polarization, III-nitride devices grown on nonpolar and semipolar orientations have become a major area of research. In addition to the reduction in the polarization-induced internal electric field, semipolar orientations potentially offer the possibility of higher indium incorporation, which is necessary for the emission of light in the visible range and is the preferred growth orientation for green/yellow light-emitting diodes and lasers. This review presents the recent progress on the development of semipolar InGaN quantum well laser diodes. The developments of laser diodes in three different semipolar planes such as (11–22), (20–21), and (20–2–1) planes are discussed including the bright prospects of group III-nitrides.

Engineering of electric field distribution in GaN(cap)/AlGaN/GaN heterostructures: theoretical and experimental studies

Polarization engineering of GaN-based heterostructures opens a way to develop advanced transistor heterostructures, although measurement of the electric field in such heterostructures is not a simple task. In this work, contactless electroreflectance (CER) spectroscopy has been applied to measure the electric field in GaN-based heterostructures. For a set of GaN(d = 0, 5, 15, and 30 nm)/AlGaN(20 nm)/GaN(buffer) heterostructures a decrease of electric field in the GaN(cap) layer from 0.66 MV cm−1 to 0.27 MV cm−1 and an increase of the electric field in the AlGaN layer from 0.57 MV cm−1 to 0.99 MV cm−1 have been observed with the increase in the GaN(cap) thickness from 5–30 nm. For a set of GaN(20 nm)/AlGaN(d = 10, 20, 30, and 40 nm)/GaN(buffer) heterostructures a decrease of the electric field in the AlGaN layer from 1.77 MV cm−1 to 0.64 MV cm−1 and an increase of the electric field in the GaN layer from 0.57 MV cm−1 to 0.99 MV cm−1 were observed with the increase in the AlGaN thickness from 10–40 nm. To determine the distribution of the electric field in these heterostructures the Schrödinger and Poisson equations are solved in a self-consistent manner and matched with experimental data. It is shown that the built-in electric field in the GaN(cap) and AlGaN layers obtained from measurements does not reach values of electric field resulting only from polarization effects. The measured electric fields are smaller due to a screening of polarization effects by free carriers, which are inhomogeneously distributed across the heterostructure and accumulate at interfaces. The results clearly demonstrate that CER measurements supported by theoretical calculations are able to determine the electric field distribution in GaN-based heterostructures quantitatively, which is very important for polarization engineering in this material system.

Influence of barrier material on spin splitting due to inversion asymmetry in heterostructures

Influence of barrier material on the spin splitting of conduction subbands in heterostructures because of structure inversion asymmetry (Bychkov–Rashba splitting) is studied. The spin splitting at a vanishing magnetic field is calculated for two heterostructures: InAs/SiO2 and InAs/In0.8Al0.2As, having the same well material InAs but very different barrier materials. It is demonstrated that the barrier material strongly influences the spin splitting of the ground conduction subband in InAs. The spin splittings for both heterostructures are computed as functions of electron density, we obtain the splitting in InAs/SiO2 almost twice larger than that in InAs/In0.8Al0.2As. The influence of spin-dependent part of the boundary conditions on the spin spin splitting is studied and it is shown that for considered heterostructures it changes the splitting up to 25% of its value. It is emphasized that the Bychkov–Rashba spin splitting is not proportional to the average electric field in heterostructure.

Rashba precession in quantum wires with interaction

Rashba precession of spins moving along a one-dimensional quantum channel is calculated, accounting for Coulomb interactions. The Tomonaga-Luttinger model is formulated in the presence of spin-orbit scattering and solved by Bosonization. Increasing interaction strength at decreasing carrier density is found to enhance spin precession and the nominal Rashba parameter due to the decreasing spin velocity compared with the Fermi velocity. This result can elucidate the observed pronounced changes of the spin splitting on applied gate voltages that are estimated to influence the interface electric field in heterostructures only a little.