Institute of Bingzhou

China

Institute of Bingzhou

China
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Du Y.,Nanjing Institute of Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Zhang J.,Nanjing Institute of Technology | And 4 more authors.
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2011

The band structure, density of states and E-Mulliken population of wurtzite GaN are calculated systematically before and after Mg doping by using the first-principles plane-wave pseudopotential method, based on the density function theory. The dielectric function, refractive index, absorption spectra, reflective spectra and optical conductivity of wurtzite GaN are analyzed and compared before and after Mg doping. The results show that the Fermi level of GaN comes into the valence band, the density of states shift towards higher energy area, carrier concentration increases significantly; the change of GaN to p-type is achieved after Mg doping. The Mg doping is found to weaken the covalent bond around, and enhance the ionicity and decrease the system stability. It is found that the influence of Mg doping to the optical properties of GaN is greater in visible light area (1.7 ~ 3.1 eV) than in high-energy area. The doping increases static dielectric constant, and enhances photoconductivity.


Du Y.,Nanjing Institute of Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Fu X.,Nanjing Institute of Technology | And 2 more authors.
Optik | Year: 2012

Using research on the negative electron affinity GaN photocathode photoemission mechanism, we obtained the reflective-type and transmission-type GaN photocathode quantum efficiency formulas. The influence on quantum efficiency and sensitivity of integral of cathode performance parameters such as electron surface escape probability P, electron diffusion length L D, absorption coefficient α, back-interface recombination rate S v and cathode thickness T e, were analyzed using these formulas. It was found that to obtain negative electron affinity GaN optoelectronic cathodes with high quantum efficiencies, we must constantly improve cathode activation technologies and the surface escaping probability of cathode. Also, we must increase the electronic diffusion length, reduce the rate of compounding, and find the optimal thickness of the cathode transmit layer based for the specific electronic diffusion length. © 2011 Elsevier GmbH. All rights reserved.


Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Fu X.,Nanjing Institute of Technology | Wang X.,Nanjing Institute of Technology | Wang M.,Ludong University
Optik | Year: 2012

The band structure, density of states and optical properties of zinc-blende GaN are calculated systematically by using the first-principles plane-wave pseudopotential method, based on the density function theory. Results show that zinc-blende GaN is a typical direct band gap semiconductor. The band gap is 1.496 eV, the valence bands are attributed to Ga3d, N2s and N2p electronic states, and the conduction bands are attributed to Ga4s and Ga4p electronic states. The electrical transport properties and types of carriers of GaN are attributed to N2p and Ga4s electronic states near the Fermi level. The static dielectric constant ε 1(0) = 3.9065 eV, the refractive index n0=1.9765eV, and the maximum peak of absorption coefficient is 354655.6 cm -1. The dielectric function, refractive index, absorption spectra, reflective spectra, optical conductivity and energy loss function are calculated using band structure and density of states. This provides a theoretical basis for the design and application of GaN opto-electronic materials. © 2011 Elsevier GmbH.


Yu X.,Nanjing Institute of Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Ge Z.,Nanjing Institute of Technology | And 3 more authors.
Applied Surface Science | Year: 2013

Using quantum mechanics GASTEP software package based on the first principle density function theory (DFT), the electronic structure and optical properties of Ga0.5Al0.5As(1 0 0) β2(2 × 4) reconstruction surface are calculated. Result shows that Ga 0.5Al0.5As(1 0 0) β2(2 × 4) reconstruction surface is stable. The calculated work function of Ga 0.5Al0.5As(1 0 0) β2(2 × 4) reconstruction surface is 4.811 eV. The band gap of the surface is smaller than the bulk. During the formation of the surface, the electrons move into the bulk and a band-binding region is formed. The absorption peaks move to the high-energy edge and the reflectivity decreases, the static dielectric constant decreases, metal reflective properties region of the surface moves to the low-energy edge and is smaller than the bulk. © 2012 Elsevier B.V. All rights reserved.


Yu X.,Nanjing Institute of Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Ge Z.,Nanjing Institute of Technology | And 2 more authors.
Optik | Year: 2013

Using quantum mechanics GASTEP software package based on the first principle density function theory, the electronic structure and optical properties of Ga1-xAlxAs at different Al constituent are calculated. Result shows that with the increase of Al constituent, the band gap of Ga1-xAlxAs increases and varies from direct band gap to indirect band gap; the absorption band edge and the absorption peak move to high-energy side; the static reflectivity decreases. With the increasing of the incident photon energy, Ga1-xAlxAs shows metal reflective properties in certain energy range. With the increasing of Al constituent, static dielectric constant decreases and the intersection of dielectric function and the x-axis move towards high-energy side; the peak of energy loss function move to low-energy side and the peak value reduces. © 2013 Elsevier GmbH.


Du Y.,Nanjing Institute of Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing Institute of Technology | Fu X.,Nanjing Institute of Technology | And 2 more authors.
Proceedings - 2010 8th International Vacuum Electron Sources Conference and Nanocarbon, IVESC 2010 and NANOcarbon 2010 | Year: 2010

Based on the negative electron affinity (NEA) GaN ultraviolet photocathode has high sensitivity, small dark emission, concentrative energy distribution of the launched electron, wide direct band gap, high quantum efficiency launch, solar blind response and so on, it is the extremely ideal new ultraviolet photocathode. In recent years it has been widely applied in the weak ultraviolet survey domain such as scientific research, military, outer space, environmental protection and so on[1]. The quantum efficiency is an important parameter it attributes the photocathode characteristic and makes us understand thoroughly the photoelectric emission mechanism. Quantum efficiency formula of reflective and transmission GaN optoelectronic cathode can be obtained by solving the diffusion equation of heat electron consistency, through the theoretical formula we can further study the effect of P, electronic diffusion length LD, absorption coefficient α, compound rate of back interface Sv and thickness of cathode transmit layer Te as the cathode performance parameters to Quantum efficiency [2-4]. © 2010 IEEE.


Du Y.,Nanjing University of Science and Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing University of Science and Technology | Wang H.,Nanjing University of Science and Technology | And 3 more authors.
Chinese Optics Letters | Year: 2012

We employ plane-wave with ultrasoft pseudopotential method to calculate and compare the total density of states and partial density of states of bulk-phase GaN, Ga 0.9375N, and GaN 0.9375 systems based on the first-principle density-functional theory (DFT). For Ga and N vacancies, the electronic structures of their neighbor and next-neighbor atoms change partially. The G 0.9375N system has n-type semiconductor conductive properties, whereas the GaN 0.9375 system has p-type semiconductor conductive properties. By studying the optical properties, the influence of Ga and N vacancy defects on the optical properties of GaN has been shown as mainly in the low-energy area and very weak in high-energy area. The dielectric peak influenced by vacancy defects expands to the visible light area, which greatly increases the electronic transition in visible light area. © 2012 Chinese Optics Letters.


Du Y.,Nanjing University of Science and Technology | Du Y.,Institute of Bingzhou | Chang B.,Nanjing University of Science and Technology | Wang X.,Nanjing University of Science and Technology | And 3 more authors.
Applied Surface Science | Year: 2012

The adsorption characteristics and change in work function of Cs on a (2 × 2) GaN(0 0 0 1) surface with a coverage from 1/4 to 1 monolayer (ML) have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The results show that the most stable positions of Cs adatoms on GaN(0 0 0 1) surfaces are at N-bridge and H3 sites for 1/4 ML coverage. As the Cs atomic coverage is increased, adsorption energy and stability reduce and achieve saturation when the Cs adatom coverage is 3/4 ML. The transfer of Cs6s electrons to Ga atoms in the outermost layer decreases the work function of the system. © 2012 Elsevier B.V. All rights reserved.


Du Y.-J.,Institute of Bingzhou | Du Y.-J.,Nanjing University of Science and Technology | Chang B.-K.,Nanjing University of Science and Technology | Zhang J.-J.,Nanjing University of Science and Technology | And 2 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2012

The band structure, the density of states, the surface energy, the work function, and the optical properties of GaN(0001)(2×2) clean surface are calculated systematically by the first-principles plane-wave ultro-soft pseudopotential method based on the density function theory. It is found that the band structure of GaN(0001) surface changes greatly after relaxation, the surface has metallic conductive properties, and there is obvious surface state near the bottom of conduction band. In the effect of dipole moment, the surface charges shift and Ga-terminated surface is positive polar surface. the surface energy and the work function of GaN (0001) surface are obtained to be 2.1 J·m -2 and 4.2 eV, respectively. The optical properties of GaN (0001) surface and bulk phase GaN are analyzed and compared. It is found that there is big difference between them. © 2012 Chinese Physical Society.


Du Y.-J.,Institute of Bingzhou | Du Y.-J.,Nanjing University of Science and Technology | Chang B.-K.,Institute of Bingzhou | Wang H.-G.,Institute of Bingzhou | And 2 more authors.
Chinese Physics B | Year: 2012

The adsorption characteristics of Cs on GaN (0001) and GaN (0001) surfaces with a coverage from 1/4 to 1 monolayer have been investigated using the density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The results show that the most stable position of the Cs adatom on the GaN (0001) surface is at the N-bridge site for 1/4 monolayer coverage. As the coverage of Cs atoms at the N-bridge site is increased, the adsorption energy reduces. As the Cs atoms achieve saturation, the adsorption is no longer stable when the coverage is 3/4 monolayer. The work function achieves its minimum value when the Cs adatom coverage is 2/4 monolayer, and then rises with Cs atomic coverage. The most stable position of Cs adatoms on the GaN (0001) surface is at H3 site for 1/4 monolayer coverage. As the Cs atomic coverage at H3 site is increased, the adsorption energy reduces, and the adsorption is still stable when the Cs adatom coverage is 1 monolayer. The work function reduces persistently, and does not rise with the increase of Cs coverage. © 2012 Chinese Physical Society and IOP Publishing Ltd.

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