Reanalysis of energy band structure in the type-II quantum wells

Band structure analysis holds significant importance for understanding the optoelectronic characteristics of semiconductor structures and exploring their potential applications in practice. For quantum well structures, the energy of carriers in the well splits into discrete energy levels due to the confinement of barriers in the growth direction. However, the discrete energy levels obtained at a fixed wave vector cannot accurately reflect the actual energy band structure. In this work, the band structure of the type-II quantum wells is reanalyzed. When the wave vectors of the entire Brillouin region(corresponding to the growth direction) are taken into account, the quantized energy levels of the carriers in the well are replaced by subbands with certain energy distributions. This new understanding of the energy bands of low-dimensional structures not only helps us to have a deeper cognition of the structure, but also may overturn many viewpoints in traditional band theories and serve as supplementary to the band theory of low-dimensional systems.

Energy Band Structure of Alq_3/TCAQ Heterostructure Complex Film Determined by Surface Photovoltage Spectroscopy(SPS)

8-Hydroxyquinoling aluminum (Alq3) and 11, 11, 12, 12-tetracyano-9, 10-anthraquino dimethane(TCAQ) monolayer films and their heterostructure complex films were prepared by a vacuum deposition method. By means of surface photovoltage spectroscopy (SPS) and electric field-induced surface photovoltage spectroscopy (EFISPS), the band gaps of TCAQ and Alq3 monolayer films and the properties of the Alq3/TCAQ bilayer film were investigated. By analysing the mechanism and the results of the SPS and the EFISPS, a reasonable energy band structure of the Alq3/TCAQ complex film was roughly determined.

Studying the variable energy band structure for energy storage materials in charge/discharge process

So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-green-blue(RGB)value,reflectivity,transmittance,UV-vis,XPS,UPS)to studyα-Co(OH)_(2) electrode working in KOH electrolyte as the research object,we provide direct experimental evidence that:(1)The intercalation of OH-ions will reduce the valence/conduction band(VB and CB)and band gap energy(Eg)values;(2)The deintercalation of OH-ions corresponds with the reversion of VB,CB and E_(g) to the initial values;(3)The color of Co(OH)_(2) electrode also exhibit regular variations in RGB value during the charge-discharge process.

Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi_2Sr_2CaCu_2O_(8＋δ) Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

We carry out detailed momentum-dependent and temperature-dependent measurements on Bi_2Sr_2CaCu_2O_（8＋δ）（Bi2212） superconductor in the superconducting and pseudogap states by super-high resolution laser-based angleresolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212（T_c= 91 K） at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form（cos（2Φ））. It can be alternatively fitted by including a high-order term（cos（6Φ）） in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogap temperature without a signature of band reorganization which is distinct from that found in Bi_2Sr_2CuO_（6＋δ） superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors.These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.

The Influence of Muffin-tin Approximation on Energy Band Gap

ＩｎｔｒｏｄｕｃｔｉｏｎＳｉｎｃｅｉｔｓｐｒｅｓｅｎｔａｔｉｏｎ，ＬＭＴＯ－ＡＳＡ（ＬｉｎｅａｒＭｕｆｉｎ－ＴｉｎＯｒｂｉｔａｌ－ＡｔｏｍｉｃＳｐｈｅｒｅＡｐ－ｐｒｏｘｉｍａｔｉｏｎ）ｈａｓｂｅｅｎｗｉｄｅｌｙａｐｐｌｉｅｄｔｏｓｏｌｖｉｎｇｔｈｅｐ...

First-principle calculation on the defect energy level of carbon vacancy in 4H-SiC

First, electronic structures of perfect wurtzite 4H-SiC were calculated by using first-principle ultra-soft pseudopotential approach of the plane wave based on the density functional theory; and the structure changes, band structures, and density of states were studied. Then the defect energy level of carbon vacancy in band gap was examined by substituting the carbon in 4H-SiC with carbon vacancy. The calculated results indicate the new defect energy level generated by the carbon vacancy, and its location in the band gap in 4H-SiC, which has the character of deep acceptor. A proper explanation for green luminescence in 4H-SiC is given according to the calculated results which are in good agreement with our measurement results.

Exploring the band structure of Wurtzite InAs nanowires using photocurrent spectroscopy

Nano Research volume We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs.Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory.The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate.From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs.This information is vital to the development of crystal phase engineering of this important III-V semiconductor.

Novel photoluminescence properties of InAlO_3(ZnO)_m superlattice nanowires

One-dimension InAlO3 （ZnO）m superlattice nanowires were successfully synthesized via chemical vapor deposition. Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the （0001） direction. The photoluminescence properties of InAlO3（ZnO）m superlattice nanowires are studied for the first time. The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states. The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region. A new luminescence mechanism is proposed, combined with the special energy band structure of InAlO3（ZnO）m.

Morphology-structure diversity of ZnS nanostructures and their optical properties

ZnS nanostructures with different dimensions and structure-related properties were reviewed in this paper. The crystallization of nanostructures from 0D, 1D to 3D, as well as the heterogonous counterparts, was sum- marized in the aspect of zinc blende, wurtzite structure, and their combinations. Furthermore, the structure-related energy bands and the corresponding photoelectric properties of ZnS nanostructures were also focused, in which we made a brief summary of the co-relations between photoluminescence and crystallography, especially the defectrelated luminescence properties of ZnS nanocrystal.

Lower oxygen vacancy concentration in BiPO_(4)with unexpected higher photocatalytic activity

Defect engineering has been demonstrated to be an appealing strategy to boost the photocatalytic activity of materials.However,can higher defect concentration bring about higher photocatalytic activity?This is an open question.In this work,BiPO_(4)photocatalysts with controllable oxygen vacancy concentrations were successfully synthesized.The photocatalytic activity of the obtained BiPO_(4)photocatalysts was determined by the removal of ciprofloxacin and 4-chlorophenol,as well as CO_(2)photoreduction.The BiPO4materials with lower oxygen vacancy concentration could display unexpected higher photocatalytic efficiency.Through the investigation of different factors which may affect the photocatalytic performance,such as crystal structure,morphology,specific surface area,defect,and energy band structure,it can be found that the energy band structure difference was responsible for the enhanced photocatalytic activity.

Constructing heterointerface of Bi/Bi_(2)S_(3)with built-in electric field realizes superior sodium-ion storage capability

Bismuth sulfide(Bi_(2)S_(3))is a dominant anode material for sodium-ion batteries due to its high theoretical capacity.However,extreme volume fluctuations as well as low electrical conductivity and reaction kinetics still limit its practical applications.Herein,we construct an abundant heterointerface of Bi/Bi_(2)S_(3)by engineering the structure of Bi nanoparticles embedded on Bi_(2)S_(3)nanorods(denoted as Bi-Bi_(2)S_(3)NRs)to effectively solve the above-mentioned obstacles.Theoretical and systematic characterization results reveal that the constructed hetero-interface of Bi/Bi_(2)S_(3)has a built-in electric field,significantly boosts the electrical conductivity,enhances the Na^(+)diffusion kinetics,and buffers the volume variation.With this modification,it can deliver long cycling life,with an ultra-high capacity of 500 mAh g^(-1)over 500 cycles at 1 A g^(-1),and outstanding rate capability,with a capacity of 456 mAh g^(-1)even at 15 A g^(-1).Moreover,a full cell can achieve a high energy density of 180 Wh kg^(-1)at a power density of 40 W kg^(-1).Our research opens up a fresh path for improving the dynamics and structural stability of metal sulfide-based electrode materials for SIBs.

Bending strain effects on the optical and optoelectric properties of GaN nanowires

Elastic strain has been an important method to regulate the electronic structures and physical properties of nanoscale semiconductors due to the promising potentials in improving the performance of their optoelectronic devices.Here,we report the investigation of bending strain effects on the optical and optoelectric properties of individual gallium nitride(GaN)nanowires(NWs).By charactering the near-band emission spectrum of individual GaN NWs at different bending strains with low temperature cathodoluminescence(CL),we reveal that the near-band emission splits into two peaks,where the low energy peak displays a linear redshift with increasing the bending strain while the high energy one shows a slight blueshift.Further localized ultraviolet(UV)photoresponse measurements illustrate that the photoresponse of the GaN NWs shows a linear increase with the bending train,and the maximum enhancement is more than two orders of magnitude.The experimental observations are well interpreted by theoretical calculations on the strain modulation on the electronic band structure of GaN combined with analysis of carrier dynamics and optical waveguide effect in the bending strain field.Our results not only shed light on the bending strain effects on the optical and optoelectric properties of semiconductors,but also hold potential to help the future design of high performance nano-optoelectric devices.