Two dimensional GeO2/MoSi2N4 van der Waals heterostructures with robust type-II band alignment

Constructing two-dimensional (2D) van der Waals heterostructures (vdWHs) can expand the electronic and optoelectronic applications of 2D semiconductors. However, the work on the 2D vdWHs with robust band alignment is still scarce. Here, we employ a global structure search approach to construct the vdWHs with monolayer MoSi₂N₄ and wide-bandgap GeO₂. The studies show that the GeO₂/MoSi₂N₄ vdWHs have the characteristics of direct structures with the band gap of 0.946 eV and type-II band alignment with GeO₂ and MoSi₂N₄ layers as the conduction band minimum (CBM) and valence band maximum (VBM), respectively. Also, the direct-to-indirect band gap transition can be achieved by applying biaxial strain. In particular, the 2D GeO₂/MoSi₂N₄ vdWHs show a robust type-II band alignment under the effects of biaxial strain, interlayer distance and external electric field. The results provide a route to realize the robust type-II band alignment vdWHs, which is helpful for the implementation of optoelectronic nanodevices with stable characteristics.     

Tunable band gap and optical properties of surface functionalized Sc_2C monolayer

Using the density functional theory, we have investigated the electronic and optical properties of two-dimensional Sc_2C monolayer with OH, F, or O chemical groups. The electronic structures reveal that the functionalized Sc_2C monolayers are semiconductors with a band gap of 0.44–1.55 eV. The band gap dependent optical parameters, like dielectric function, absorption coefficients, reflectivity, loss function, and refraction index were also calculated for photon energy up to 20 eV. At the low-energy region, each optical parameter shifts to red, and the peak increases obviously with the increase of the energy gap. Consequently, Sc_2C monolayer with a tunable band gap by changing the type of surface chemical groups is a promising 2D material for optoelectronic devices.     

Photodetecting and light-emitting devices based on two-dimensional materials

Two-dimensional(2D) materials, e.g., graphene, transition metal dichalcogenides(TMDs), and black phosphorus(BP), have demonstrated fascinating electrical and optical characteristics and exhibited great potential in optoelectronic applications. High-performance and multifunctional devices were achieved by employing diverse designs, such as hybrid systems with nanostructured materials, bulk semiconductors and organics, forming 2D heterostructures. In this review,we mainly discuss the recent progress of 2D materials in high-responsive photodetectors, light-emitting devices and single photon emitters. Hybrid systems and van der Waals heterostructure-based devices are emphasized, which exhibit great potential in state-of-the-art applications.     

纳米半导体中多重激子效应研究进展

多重激子效应是指纳米半导体吸收一个高能光子后产生两个甚至多个电子-空穴对的物理过程,不仅具有重要的基础研究意义,而且在新型太阳电池及高性能光电子器件领域具有潜在应用价值.综述了多重激子效应的发展历程;总结了纳米半导体的材料组分、体系结构甚至表面质量对多重激子效应的影响;介绍了多重激子效应的实验测试分析方法以及解释多重激子效应的理论方法;概括了目前多重激子效应在器件中的应用并对其应用前景进行展望.     

Hydrides as materials for semiconductor electronics

Systematic studies using density functional theory have shown that some hydrides possess the features of semiconductors. These features include larger fundamental band gap, well dispersed bottom-most conduction band and/or top-most valence band, small electron/hole effective masses and small intrinsic carrier concentration. It is demonstrated that depending upon the composition, hydrides possess a wide range of band gap values and hence they can be regarded as materials for narrow to wide band gap semiconducting applications. The possibility of designing hydride-based p–n junctions, and also their advantages as well as deficiencies compared to existing oxide semiconductors, are discussed. Replacing oxide-based semiconductors by hydrides can help to avoid problems such as formation of an oxide layer, band offsets, large concentration of defect states at the interface between the oxide and semiconductor, etc. Moreover, hydrides can be regarded as an alternative to conventional semiconductors and hence can be used in future-generation electronic devices called “hydride electronics”.     

单层SbAs和BiSb的表面修饰调控

基于密度泛函理论的第一性原理计算,研究了V族二维层状材料SbAs和BiSb在全氢化和全氟化后体系的晶体结构、稳定性和电子结构.计算结果表明,全氢化后SbAs和BiSb由buckled结构转变为准平面结构,而全氟化后则转变为low-buckled结构.同时,本征、全氢化和全氟化的SbAs和BiSb均具有很好的稳定性,具备实验合成的可能性.电子结构的分析表明,全氢化和全氟化后SbAs和BiSb均由宽带隙半导体转变为窄带隙的直隙半导体,且其能带结构仍具有很好的线性色散.通过对准平面和low-buckled结构SbAs和BiSb电子结构的进一步分析,揭示了全氢化和全氟化后体系能带变化的原因.在h-BN衬底上的计算结果显示,由于两者间的弱耦合作用,使得全氢化和全氟化SbAs的直隙半导体特征得以保留,表明其在未来光电子设备等领域中具有广泛的应用前景.     

Functionalizing AlN monolayer with hydroxyl group: Effect on the structural and electronic properties

Two-dimensional (2D) materials play key role in designing and fabricating diminutive optoelectronic devices with high efficiency. In this paper, we report the results of a comprehensive first-principles study on the structural and electronic properties of the pristine and hydroxyl group OH-functionalized (OH-AlN-OH) AlN monolayer. GGA-PBE and hybrid HSE06 functionals are employed to describe the exchange-correlation potential. According to our calculations, the pristine AlN monolayer has a wide indirect band gap of 2.954(4.000) eV determined by PBE(HSE06) level of theory. Indirect-direct gap transition is obtained through the chemical functionalization and the band gap reduces to 0.775(2.125) eV. Results shows that the OH-AlN-OH monolayer is more suitable for optoelectronic applications. Finally, the strain is proven to be efficient factor to tune the electronic properties of the studied monolayers.     

Strain drived band aligment transition of the ferromagnetic VS_2/C_3N van der Waals heterostructure

Exploring two-dimensional(2 D) magnetic heterostructures is essential for future spintronic and optoelectronic devices.Herein,using first-principle calculations,stable ferromagnetic ordering and colorful electronic properties are established by constructing the VS_2/C_3 N van der Waals(vdW) heterostructure.Unlike the semiconductive properties with indirect band gaps in both the VS_2 and C_3 N monolayers,our results indicate that a direct band gap with type-Ⅱ band alignment and p-doping characters are realized in the spin-up channel of the VS_2/C_3 N heterostructure,and a typical type-Ⅲband alignment with a broken-gap in the spin-down channel.Furthermore,the band alignments in the two spin channels can be effectively tuned by applying tensile strain.An interchangement between the type-Ⅱ and type-Ⅲ band alignments occurs in the two spin channels,as the tensile strain increases to 4%.The attractive magnetic properties and the unique band alignments could be useful for prospective applications in the next-generation tunneling devices and spintronic devices.     

Where science fiction meets reality? With oxide semiconductors!

Transparent electronics is today one of the most advanced topics for a wide range of device applications, where the key components are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive components but also as active components similar to what we observe in conventional semiconductors. As passive components they include the use of these materials as dielectrics for a wide range of electronic devices and also as transparent electrical conductors for use in several optoelectronic applications, such as liquid crystal displays, organic light emitting diodes, solar cells, optical sensors etc. As active materials, they exploit the use of truly electronic semiconductors where the main emphasis is being put on transparent thin film transistors, light emitting diodes, lasers, ultraviolet sensors and integrated circuits among others.

     

半导体物理效应与光电子高技术产业

阐述了能带理论和晶格动力学的创建对半导体科学技术发展发展的历史意义，重点介绍了若干关键半导体物理效应的内涵及其对光电子器件与技术发展所作出的源头性贡献，描绘了以半导体激光器为代表的现代光电子高科技产业的发展现状与趋势，指出了光电子高科技持续发展的主要方向。     

First-principles calculation of electronic structure of MgxZn1-xO codoped with aluminium and nitrogen

Aiming at developing p-type semiconductors and modulating the band gap for photoelectronic devices and band engineering, we present the ab initio numerical simulation of the effect of codoping ZnO with Al, N and Mg on the crystal lattice and electronic structure. The simulations are based on the Perdew--Burke--Ernzerhof generalised-gradient approximation in density functional theory. Results indicate that electrons close to the Fermi level transfer effectively when Al, Mg, and N replace Zn and O atoms, and the theoretical results were consistent with the experiments. The addition of Mg leads to the variation of crystal lattice, expanse of energy band, and change of band gap. These unusual properties are explained in terms of the computed electronic structure, and the results show promise for the development of next-generation photoconducting devices in optoelectronic information science and technology.     

Carrier generation and recombination rate in armchair graphene nanoribbons

Armchair graphene nanoribbons (A-GNRs), with a tunable energy gap, are an alternative structure for use in optoelectronic devices. The performance of these optoelectronic devices critically depends on the carrier generation and recombination rates, which have been calculated in this paper. Because of the 1D band structure of A-GNRs, carrier scattering, generation and recombination rates in these structures would be completely different from those in 2D graphene sheets. In this paper, using the tight binding model, and by considering the edge deformation and Fermi golden rule, we find the band structure, and the carrier generation and recombination rates for pure A-GNR due to optical and acoustic phonons, as well as Line Edge Roughness (LER) scatterings. The obtained results show that the total generation and recombination rates increase with increasing A-GNR width and eventually saturate for wide ribbons. These rates increase as the carrier concentration is increased (which has been considered homogenous along ribbon width) and temperature. Also, despite the large LER scattering in narrow ribbons, the generation and recombination rates are less for A-GNRs than for graphene sheets. Using this theoretical model, one can find the suitable A-GNR structure for the design of optoelectronic devices.     

Energy band engineering of flexible gallium arsenide through substrate cracking with pre‐tensioned films

Flexible electronics based on the otherwise rigid conventional crystalline semiconductors is emerging as a new class of technology. However, the existing layer‐transfer approaches for implementing such technologies is mostly focused on maintaining the performance of the original device. Here we show that layer transfer through substrate cracking with a pre‐tensioned nickel film readily enables the manipulation of the electronic band structure in flexible gallium arsenide (GaAs) devices. We empirically and theoretically quantify the effect of ‘engineered' residual strain on the electronic band structure in these flexible GaAs devices. Photoluminescence and quantum efficiency measurements indicate the widening of the GaAs energy bandgap due to the residual compressive strain. The experimental results are in good agreement with our theoretical calculations. This study introduces a new way for strain engineering in flexible compound semiconductors with important implications for electronic and optoelectronic applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Co和Mn共掺杂ZnO铁磁性的第一性原理

基于密度泛函理论(DFT)的总体能量平面波超软赝势方法,结合广义梯度近似(GGA),对Co单独掺杂ZnO和(Co,Mn)共掺杂ZnO的32原子超原胞体系进行了几何结构优化,计算了纤锌矿结构ZnO、Co-ZnO及(Co,Mn)共掺杂ZnO的能带结构、电子态密度,并对此进行了详细的分析。计算结果表明,ZnO中单独掺杂Co元素显示出铁磁性行为,Mn的引入减弱了Co-ZnO的铁磁性。     

Monolayered semiconducting GeAsSe and SnSbTe with ultrahigh hole mobility

High carrier mobility and a direct semiconducting band gap are two key properties of materials for electronic device applications. Using first-principles calculations, we predict two types of two-dimensional semiconductors, ultrathin GeAsSe and SnSbTe nanosheets, with desirable electronic and optical properties. Both GeAsSe and SnSbTe sheets are energetically favorable, with formation energies of −0.19 and −0.09 eV/atom, respectively, and have excellent dynamical and thermal stability, as determined by phonon dispersion calculations and Born–Oppenheimer molecular dynamics simulations. The relatively weak interlayer binding energies suggest that these monolayer sheets can be easily exfoliated from the bulk crystals. Importantly, monolayer GeAsSe and SnSbTe possess direct band gaps (2.56 and 1.96 eV, respectively) and superior hole mobility (~20 000 cm²·V⁻¹·s⁻¹), and both exhibit notable absorption in the visible region. A comparison of the band edge positions with the redox potentials of water reveals that layered GeAsSe and SnSbTe are potential photocatalysts for water splitting. These exceptional properties make layered GeAsSe and SnSbTe promising candidates for use in future high-speed electronic and optoelectronic devices.     

Prediction of 2D Li2X (X=Se,Te) monolayer semiconductors by first principles calculations

Two dimensional monolayer materials play important roles in new generation of electronic and optical devices in nano scale. In this paper, by using first principles calculations, the existence of 2D Li₂X (X=Se, Te) monolayer materials are theoretically predicted. Through cohesive energy calculation and phonon dispersion simulation, it is proved that the proposed 2D Li₂Se and Li₂Te monolayer materials are energetically and dynamically stable suggests their potential experimental realization. Our study shows that these newly predicted compounds are direct semiconductors and have strain tunable wide band gaps. As direct semiconductors, these new monolayers may have many applications in electronics and optoelectronics devices.     

Organic materials in future integrated optoelectronic circuits

During the last two decades, lithium niobate has been extensively studied for applications in integrated optical circuits. However, it is difficult to integrate lithium niobate optical devices with semiconductor electronic devices because the materials are incompatible. In recent years, semiconductor materials have been emerging as the main contenders in applications; these materials have the advantage of allowing both optical and electronic devices to be integrated. Further, the semiconductor technology has advanced rapidly, allowing us to engineer device parameters very precisely. In semiconductor optoelectronic devices, that is, bulk and quantum well structures, electroabsorption has mainly been used for amplitude modulation of light. The electrorefraction effect is the most useful for devices employing phase-modulation techniques, but this effect cannot be effectively utilized in semiconductors since the strongest electrorefraction effect is near the absorption edge of the material. Recently, organic materials have been shown to have electro-optic coefficients equal to or larger than that of lithium niobate. There are major advantages of organic materials: (1) the organics can be deposited on semiconductor substrates, and therefore both electronic and optical circuits can be integrated; (2) in organic materials the electrorefraction can be effectively utilized to obtain both amplitude and phase modulation; (3) the organic material composition can be adjusted to satisfy some device requirements. In this paper, a comparison of these material systems are made in terms of device applications.     

Research progress of rubrene as an excellent multifunctional organic semiconductor

Rubrene,a superstar in organic semiconductors,has acliieved imprecedented achievements in the application of electronic devices,and research based on its various photoelectric properties is still in progress.In this review,we introduced the preparation of rubrene crystal,summarized the applications in organic optoelectronic devices with the latest research achievements based on rubrene semiconductors.An outlook of future research directions and cliallenges of rubrene semiconductor for applications is also provided.     

III–V semiconductor interface properties as a knowledge basis for modern heterostructure devices

Some examples of interface studies are reported which show their close link with progress in III–V modern semiconductor device physics and technology. The surface electronic properties investigated in-situ by reflectance anisotropy spectroscopy during InGaP/InP growth (metal-organic vapor-phase epitaxy) are essential for the control of ordering phenomena in these layers, which is relevant for high-performance optoelectronic devices. Studies of electronic interface states at metal/narrow-gap III–V semiconductors are presented, which enabled the successful preparation of semiconductor/superconductor hybrid devices. For group-III nitrides with wurtzite structure the presence of fixed polarization interface charges yields new challenges in order to understand and control Schottky-barrier heights, band offsets and 2D confinement in heterostructure field-effect transistors. Received: 26 April 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002     

The potential of n-i-p-i doping superlattices for novel semiconductor devices

In this paper we suggest a number of device applications of n-i-p-i doping superlattices. The concept of these devices is based on the unusual electronic properties of this new class of semiconductors such as extremely long excess carrier lifetime, tunable band gap and carrier concentration. Emphasis will be on high-sensitivity low-noise photodetectors, tunable lasers, optical amplifiers, and on ultrafast devices for the generation, modulation and detection of optical signals.