Comparison of Gain Properties with Electron-Electron and Electron-LO-Phonon Interactions in Quantum Cascade Structure

The gain properties of （A1N）m/（GaN）n superlattice-based quantum cascade structure axe investigated by using a nonequilibrium Green＇s function （NGF） theory. In this theory, the electron-electron interaction and electron- LO-phonon interaction axe both considered. The gain spectra of QCL axe calculated from some current-driven items, which are derived from these two interactions. The results show that the effect of the electron-electron interaction is notable in the low-photon-energy range and the electron-LO-phonon interaction only takes effect in the high-photon-energy range, where photon energy is close to or larger than LO-phonon energy of GaN materials.

Dynamics of measurement-induced non-locality and geometric discord with initial system-environment correlations

We analyze the dynamics of geometric measure of discord （GMOD） and measurement-induced non-locality （MIN） in the presence of initial system-reservoir correlations without Born and Markov approximation. Although the initial system-environment states have the same reduced density matrices for both the system and environment, the effects of different initial system-environment correlations have been shown to fundamentally alter the time evolution of GMOD and MIN between two quantum systems in both Markovian and non-Markovian regimes. In general, both GMOD and MIN experience a sudden increase for initially quantum-correlated states, and a sudden decrease for classical-correlated states before they reach the same stationary values with initially factorized states.

Influence of Si doping on the structural and optical properties of InGaN epilayers

Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction （HRXRD）, photolumimescence （PL）, scanning electron microscope （SEM）, and atomic force microscopy （AFM）. It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing tile formation of V-defects, which act as nonradiative recombination centers in the InGaN, and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.

Superhydrophilic and Wetting Behavior of TiO_(2) Films and their Surface Morphologies

TiO_(2) films,showing superhydrophilic behavior,are prepared by electron beam evaporation.Atomic force microscopy and the contact angle measurement were performed to characterize the morphology and wetting behavior of the TiO_(2) films.Most studies attribute the wetting behavior of TiO_(2) surfaces to their physical characteristics rather than surface chemistry.These physical characteristics include surface morphology,roughness,and agglomerate size.We arrange these parameters in order of effectiveness.Surface morphologies are demonstrated to be the most important.TiO_(2) films with particular morphologies show superhydrophilic behavior without external stimuli,and these thin films also show stable anti-contamination properties during cyclical wetting and drying.

Application of thermal stress model to paint removal by Q-switched Nd:YAG laser

In this paper, we demonstrate that thermal stress is the main mechanism in the process of paint removal by Q-switched Nd：YAG laser （λ = 1064 nm, τ = 10 ns）. A theoretical model ofpaint removal by short-pulse laser is established from the perspective of thermal stress. Thermal stress is generated by thermal expansion, and the temperatures of different samples are calculated according to the one-dimensional （1D） heat conduction equation. The theoretical cleaning threshold can be obtained by comparing thermal stress with the adhesion of paint, and the theoretical damage threshold is obtained by calculating the temperature. Moreover, the theoretical calculations are verified by experimental results. It is shown that the thermal stress model of the laser cleaning is very useful to choose the appropriate laser fluence in the practical applications of paint removal by Q-switched Nd： YAG laser because our model can validly balance the efficiency of laser cleaning and the safety of the substrate.

Improved light extraction of GaN-based light-emitting diodes with surface-textured indium tin oxide electrodes by nickel nanoparticle mask dry-etching

GaN-based light-emitting diodes （LEDs） with surface-textured indium tin oxide （ITO） as a transparent current spreading layer were fabricated. The ITO surface was textured by inductively coupled plasma （ICP） etching technology using a monolayer of nickel （Ni） nanoparticles as the etching mask. The luminance intensity of ITO surface-textured GaN-based LEDs was enhanced by about 34% compared to that of conventional LED without textured ITO layer. In addition, the fabricated ITO surface-textured GaN-based LEDs would present a quite good performance in electrical characteristics. The results indicate that the scattering of photons emitted in the active layer was greatly enhanced via the textured ITO surface, and the ITO surface-textured technique could have a potential application in improving photoelectric characteristics for manufacturing GaN-based LEDs of higher brightness.

High-Efficiency Saturated Red Bilayer Light-Emitting Diodes： Comparative Studies with Devices from Blend of the Same Light-Emitting Polymers

High-efficient saturated red light-emitting diodes are realized based on a bilayer of phenyl-substituted poly [p- phenylene vinylene] derivative （P-PPV） and copolymer （PFO-DBT15） of 9,9-dioctylfluorene （DOFF） and 4,7-di- 2-thienyl-2,1,3-benzothiadiazole （DBT）. External electrolurninescent （EL） quantum efficiency of PFO-DBT15 is increased from 1.6% for a single-layer device to 4.7% for the bilayer device by insertion of a P-PPV layer between PEDOT （polyethylene dioxythiophene-polystyrene sulfonic acid） and PFFO-DBT15 at the current density of 35 mA/cm^2. The luminescence efficiency reaches 0.83 cd/A, and the Commission Internationale de PEelairage coordinates （CIE） become nearly x = 0.700 and y = 0.300. In comparison with the devices from PFFO-DBT15 and P-PPV blend films, the P-PPV/PFO-DBT15 bilayer device shows higher EL quantum efficiency and better stability under high current density, The improved device performance can be attributed to the charge-confinement effect at the interface of the P-PPV/PFO-DBT15 bilayer structure.

Efficiency enhancement of an InGaN light-emitting diode with a p-AlGaN/GaN superlattice last quantum barrier

In this study, the efficiency droop of an InGaN light-emitting diode （LED） is reduced slgnlncanUy oy using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency, which is revealed by investigating the light currents, internal quantum efficiencies, energy band diagrams, carrier concentrations, carrier current densities, and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device （APSYS）.

Temperature Dependence of Raman Scattering in 4H-SiC Films under Different Growth Conditions

The microRaman scattering of 4H-SiC films, fabricated by low pressure chemical vapor deposition under different growth conditions, is investigated at temperatures ranging from 80 K to 550K. The effects of growth conditions on E2 （TO）, E1 （TO） and A1 （LO） phonon mode frequencies are negligible. The temperature dependences of phonon linewidth and lifetime of E2 （TO） modes are analyzed in terms of an anharmonic damping effect induced by thermal and growth conditions. The results show that the lifetime of E2 （TO） mode increases when the quality of the sample improves. Unlike other phone modes, Raman shift of A1 （longitudinal optical plasma coupling （LOPC）） mode does not decrease monotonously when the temperature increases, but tends to blueshift at low temperatures and to redshift at relatively high temperatures. Theoretical analyses are given for the abnormal phenomena of A1 （LOPC） mode in 4H-SiC.

GaP layers grown on GaN with and without buffer layers

The growth of GaP layer on GaN with and without buffer layers by metal-organic chemical vapour deposition （MOCVD） has been studied. Results indicate that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature （HT） GaP growth. These sites can promote the two-dimensional （2D） growth of HT GaP and reduce the surface roughness. A GaP single crystal layer grown at 680 ℃ is obtained using a 40-nm thick GaP buffer layer. The full-width at half-maximum （FWHM） of the （111） plane of GaP layer, measured by DCXRD, is 560 arcsec. The GaP layer grown on GaN without low temperature GaP buffer layer shows a rougher surface. However, the FWHM of the （111） plane is 408 arcsec, which is the indication of better crystal quality for the GaP layer grown on GaN without a low temperature buffer layer. Because it provides less nucleation sites grown at high growth temperature, the three-dimensional （3D） growth is prolonged. The crystalline quality of GaP is lightly improved when the surface of GaN substrate is pretreated by PH3, while it turned to be polycrystalline when the substrate is pretreated by TEGa.

Efficient White Light Emission Using a Single Copolymer with Red and Green Chromophores on a Conjugated Polyfluorene Backbone Hybridized with InGaN-Based Light-Emitting Diodes

We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole （BT） and 4,7-bis（2-thienyl）-2,1,3-benzothiadiazole （DBT） as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de 1＇Eclairage （CIE） coordinates, color temperature Tc and color rendering index Ra at 20mA are （0.323,0.329）, 5960K and 86, respectively. In comparison with the performance of red eopolymer PFO-DBT15 （DOF：DBT=85：15 with DOF being 9＇9- dioctylfluorene） and green copolymer PFO-BT35 （DOF：BT=-65：35） blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.

Properties of C_(60) thin film transistor based on polystyrene

This paper reports that the n-type organic thin-fihn transistors have been fabricated by using C60 as the active layer and polystyrene as the dielectric. The properties of insulator and the growth characteristic of C60 film were carefully investigated. By choosing different source/drain electrodes, a device with good performance can be obtained. The highest electron field effect mobility about 1.15 cm2/（V. s） could reach when Barium was introduced as electrodes. Moreover, the C60 transistor shows a negligible ＇hysteresis effect＇ contributed to the hydroxyl-free of insulator. The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.

A study of optical properties of a four-level atomic system via vacuum-induced coherence effects

This paper studies the effects of vacuum-induced coherence （VIC） in a four-level atomic system. The effects of VIC lead to the coherent hole burnings exhibited in the system at some certain points of the Rabi frequency. This is also the reason for the enhancement of the coherent population trapping. In addition, optical bistability occurs in the evolution curves of absorption versus the phase of Rabi frequencies.

Performance improvement of GaN-based light-emitting diode with a p-InAlGaN hole injection layer

The characteristics of a blue light-emitting diode （LED） with a p-InA1GaN hole injection layer （HIL） is analyzed numerically. The simulation results indicate that the newly designed structure presents superior optical and electrical performance such as an increase in light output power, a reduction in current leakage and alleviation of efficiency droop. These improvements can be attributed to the p-InA1GaN serving as hole injection layers, which can alleviate the band bending induced by the polarization field, thereby improving both the hole injection efficiency and the electron blocking efficiency.

Performance improvement of blue light-emitting diodes with an AlInN/GaN superlattice electron-blocking layer

The characteristics of a blue light-emitting diode （LED） with an AIlnN/GaN superlattice （SL） electron-blocking layer （EBL） are analyzed numerically. The carder concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AIInN/GaN SL EBL has better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region than the LED with a conventional rectangular AIGaN EBL or a A1GaN/GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.

Performance enhancement of an InGaN light-emitting diode with an AlGaN/InGaN superlattice electron-blocking layer

The efficiency enhancement of an InGaN light-emitting diode （LED） with an A1GaN/InGaN superlattice （SL） electron-blocking layer （EBL） is studied numerically, which involves the light-current performance curve, internal quan- tum efficiency electrostatic field band wavefunction, energy band diagram carrier concentration, electron current density, and radiative recombination rate. The simulation results indicate that the LED with an A1GaN/InGaN SL EBL has better optical performance than the LED with a conventional rectangular A1GaN EBL or a normal A1GaN/GaN SL EBL because of the appropriately modified energy band diagram, which is favorable ibr the injection of holes and confinement of elec- trons. Additionally, the efficiency droop of the LED with an AIGaN/InGaN SL EBL is markedly improved by reducing the polarization field in the active region.

Fabrication of GaN-based LEDs with 22° undercut sidewalls by inductively coupled plasma reactive ion etching

We use a simple and controllable method to fabricate GaN-based light-emitting diodes （LEDs） with 22° undercut sidewalls by the successful implementation of the inductively coupled plasma reactive ion etching （ICP-RIE）. Our exper- iment results show that the output powers of the LEDs with 22° undercut sidewalls are 34.8 rnW under a 20-mA current injection, 6.75% higher than 32.6 mW, the output powers of the conventional LEDs under the same current injection.

First-principles of wurtzite ZnO(0001) and (0001)surface structures

The surface structures ofwurtzite ZnO（0001） and（0001） surfaces are investigated by using a first-principles calculation of plane wave ultra-soft pseudo-potential technology based on density functional theory（DFT）.The calculated results reveal that the surface energy of ZnO-Zn is bigger than that of ZnO-O,and the ZnO-Zn surface is more unstable and active.These two surfaces are apt to relax inward,but the contractions of the ZnO-Zn surface are smaller than the ZnO-O surface.Due to the dispersed Zn4s states and the states of stronger hybridization between the Zn and O atoms,the ZnO-Zn surface shows n-type conduction,while the O2p dangling-bond bands in the upper part of the valence cause the ZnO-O surface to have p-type conduction.The above results are broadly consistent with the experimental results.

A GaN AlGaN InGaN last quantum barrier in an InGaN/GaN multiple-quantum-well blue LED

The advantages of a GaN-AlGaN-InGaN last quantum barrier （LQB） in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, higher recombi- nation rate, and less efficiency droop compared with conventional GaN LQBs. These improvements in the electrical and optical characteristics are attributed mainly to the specially designed GaN-AlGaN-InGaN LQB, which enhances electron confinement and improves hole injection efficiency.

Effect of n-type barrier doping on steady and dynamic performance of InGaN light-emitting diodes

The steady and dynamic properties are comparatively investigated for the n-doped and non-doped InGaN LEDs. The simulated results show that the n-doped LED exhibits the superior luminescence and modulation performance, which is mainly attributed to the higher carrier radiative rate of n-doped LED. The results can explain the reported experimental results perfectly.