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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. Source


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. Source


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. Source


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. Source


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. Source

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