Electrical and electroluminescence properties of ITO/PEDOT:PSS/TPD:Alq3:C60/Al organic light emitting diodes

Organic light emitting diodes (OLEDs) of ITO/PEDOT:PSS/TPD:Alq₃:C₆₀/Al with different C₆₀ concentrations (0-6.0 wt.%) have been fabricated. The physical parameters including electrical and optical properties of the samples have been measured by Luminance-current-voltage (L-I-V) characteristics and optical absorbance. The current-voltage characteristics indicate that field-emission tunneling injection dominates in the diodes at high applied voltages. It is found that with increasing the concentration of C₆₀, the injection barrier for holes slightly reduces and the hole’s mobility increases over two orders of magnitude. Also, electroluminescence enhances with the presence of C₆₀ in the blend; optimum current efficiency occurs at 3 wt% C₆₀. The method provides a simple way of increasing the efficiency of OLEDs.     

Saturation behavior of extrinsic photoconductivity in GaP light emitting diodes at high infrared intensities

Saturation of extrinsic photoconductivity in GaP:N(Zn, Te) diodes could be achieved by excitation with a TEA-CO₂-laser. At wavelengths in the 10 m range intensities of several 100 kW/cm² being near the damage threshold were applied. Carrier lifetimes of 60 ps at 4.2 K and 200 ps at 77 K could be estimated. The only conceivable mechanism explaining these short time constants is the capture of infrared excited holes by ionized shallow acceptors in the highly compensated p-side of the diode.     

一级相变材料Mn1.2Fe0.8P0.4Si0.6的热磁发电性能

本文报道把热能直接转换电能的热磁发电技术所用一级相变新材料Mn_1.2Fe_0.8P_0.4Si_0.6的磁性和热磁发电性能.用高能球磨机械合金化技术和固相烧结合成方法制备了Mn_1.2Fe_0.8P_0.4Si_0.6化合物.磁性测量结果表明,该化合物呈现从铁磁状态变为顺磁状态的一级相变,居里温度为337K,并伴随巨大的磁化强度的变化.根据该材料的这一特性,设计制作了热磁发电演示装置,测定了热流引起材料的相变而产生的电流,并研究了固定磁场中热致磁转变产生的电流随热流温度和样品质量的变化.研究结果表明Mn_1.2Fe_0.8P_0.4Si_0.6化合物具有很好的热磁发电性能,可作为热磁发电材料.     

Study of non-exponential electron capture by the main electron trap in GaAs0.62P0.38

In deep level transient spectroscopy (DLTS) exponentiality of level population changes in thermal emission as well as in capture processes is assumed. This is however, contrary to what is often observed in experiment. In this paper a model for interpretation of DLTS data in the case of non-exponential capture of electrons is proposed. It is assumed that the height of the capture of carrier changes locally according to the Gaussian distribution This model is applied to the case of deep electron trap with thermal activation energy equal to ΔE_B = 0.39 eV, observed in VPE GaAs_0.62P_0.38. Te. This model provides a capture barrier as well as a capture cross-section which are different from the ones predicted by the exponential transient model i.e., the ones derived from the slope of capacitance changes due to the filling pulse versus pulse duration at very short times.     

Enhancement of minority carrier lifetime in GaAs1? x P x ( x =0.4; 0.65) by nitrogen implantation

Minority carrier lifetimes in nitrogen implanted GaAs_1-x P _x (x=0.4; 0.65) were measured at 77K by an optical phase shift method as a function of nitrogen dose and annealing temperature in order to investigate the dependence of the lifetime on the concentration of nitrogen isoelectronic traps. A large increase in the lifetime was observed after nitrogen implantation followed by annealing at and above 800°C. The maximum lifetimes were 22ns for GaAs_0.35P_0.65 and 6.7 ns for GaAs_0.6P_0.4. They were obtained by implantation to a dose of 5×10¹³ cm⁻² in GaAs_0.35P_0.65 and 10¹³ cm⁻² in GaAs_0.6P_0.4. The lifetime after nitrogen implantation followed by annealing was longer by a factor of 6–7 than that of the unimplanted sample.     

Nonlinear microwave emission in Ba0.6K0.4BiO3 crystals near Tc

We report a detailed investigation of harmonic generation at microwave frequencies in Ba_0.6K_0.4BiO₃ crystals. Second- and third-harmonic signals are investigated as a function of temperature, external magnetic field and input power level, at temperatures close to T_c. The experimental data are discussed in the framework of a phenomenological theory, based on the two-fluid model, which assumes that the microwave and the static fields, penetrating the sample within the penetration depth, perturb the partial concentrations of the normal and condensate fluids. We show that the enhanced nonlinear effects detected near T_c in Ba_0.6K_0.4BiO₃ and YBa₂Cu₃O₇ crystals may have the same origin. However, in order to account for the experimental data of Ba_0.6K_0.4BiO₃, one needs to involve a distribution of T_c over the crystal.     

Influence of buffer layer thickness and epilayer’s growth temperature on crystalline quality of InAs0.6P0.4/InP grown by LP-MOCVD

InAs_0.6P_0.4 epilayers grown on InP (100) substrates using two-step growth method by LP-MOCVD were investigated. A low temperature (450 °C) In_0.18Ga_0.82As buffer layer was introduced to relax the lattice mismatch between the InAs_0.6P_0.4 epilayer and the InP substrate. The influence of In_0.18Ga_0.82As buffer layer thickness and epilayer’s growth temperature on crystalline quality of InAs_0.6P_0.4 epilayer was characterized by Scanning electron microscopy, X-ray diffraction, Hall measurements, Transmission electron microscopy and Photoluminescence. The experimental results showed that the crystalline quality of InAs_0.6P_0.4 epilayers could be greatly improved by optimizing the In_0.82Ga_0.18As buffer layer thicknesses and the InAs_0.6P_0.4 epilayer’s growth temperatures. It was found that, when In_0.82Ga_0.18As buffer layer thickness was 100 nm and InAs_0.6P_0.4 epilayer’s growth temperature was 580 °C, the InAs_0.6P_0.4 epilayer exhibited the best crystalline quality and properties.     

Nonpolar a-plane light-emitting diode with an in-situ SiNx interlayer on r-plane sapphire grown by metal-organic chemical vapour deposition

We report on the growth and fabrication of nonpolar a-plane light emitting diodes with an in-situ SiN_x interlayer grown between the undoped a-plane GaN buffer and Si-doped GaN layer. X-ray diffraction shows that the crystalline quality of the GaN buffer layer is greatly improved with the introduction of the SiN_x interlayer. The electrical properties are also improved. For example, electron mobility and sheet resistance are reduced from high resistance to 31.6 cm²/(V·s) and 460 Ω/口 respectively. Owing to the significant effect of the SiN_x interlayer, a-plane LEDs are realized. Electroluminescence of a nonpolar a-plane light-emitting diode with a wavelength of 488nm is demonstrated. The emission peak remains constant when the injection current increases to over 20 mA.     

Absorption and photoluminescent measurements in indirect,nitrogen doped GaAs1−χPχ

The absorption and photoluminescent spectra of nitrogen doped GaAs_1?χP_χ epitaxial layers were studied in the alloy composition range 0.58 ? χ ? 0.77. The structure in the absorption and luminescent spectra are analysed.     

IR investigation of the interaction of deuterium with Ce0.6Zr0.4O2 and Cl-doped Ce0.6Zr0.4O2

The interaction of deuterium with Ce_0.6Zr_0.4O₂, synthesised by a co-precipitation technique, is discussed on the basis of the sample's bulk and surface composition and the presence of trace amounts of silicon. Redox cycling resulted in surface cerium enrichment, which, however, only moderately affected the interaction of the material with D₂. Addition of a trace amount of chloride ion to the oxide surface promoted both H/D scrambling and vacancy creation. Chloride ion was also found to prevent the surface cerium enrichment induced by redox cycling.     

有机异质结连接层C60/CuPc电荷产生能力研究

有机异质结连接层因其具有良好的透光性能、制备工艺和有机电致发光器件(Organic light-emitting diodes,OLEDs)完全兼容的优点,被广泛应用于叠层OLEDs中。在叠层OLEDs中,连接层可产生电荷,其工作性能是影响叠层OLEDs性能的关键因素之一。为了获得最佳性能的有机异质结连接层,本文制备了结构为glass/ITO/tris(8-hydroxyquinoline) aluminum(Alq_3)(60 nm)/C_(60)(x nm)/CuPc(y nm)/N,N′-bis(naphthalen-1-yl)-N,N′-bis (phenyl)-be-nzidine(NPB)(40 nm)/Al (100 nm)的有机器件,直接获得了有机异质结连接层C_(60)/CuPc产生的器件电流。通过结构优化发现,结构为C_(60)(30 nm)/CuPc(10 nm)的连接层具有最强的电荷产生能力,并对最优结构连接层形成的物理机制作了合理的解释.本文获得的结果可为理解有机异质结连接层工作机理以及制备高性能叠层OLEDs提供理论基础。     

ITO/有机半导体/金属结构OLED器件的数值模拟

基于稳态的小信号漂移扩散方程,建立了有电极的单层有机电致发光(OLED)器件的数值模型,编制的MATLAB程序,首先模拟了文献中的OLED器件电极附近正电荷层(面电荷)对器件J-V的影响,得到了和文献中一致的结果. 模拟了ITO/PPV/Ca结构的OLED器件,模拟时,考虑了OLED阳极附近存在正体电荷,得到的J-V曲线和文献中的实验结果一致,体电荷产生了势垒,影响了电流曲线. 关键词： 有机电致发光 数值模拟 漂移扩散模型     

Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N量子阱中的Rashba自旋劈裂

正如人们所知, 可以通过电场或者设计非对称的半导体异质结构来调控体系的结构反演不对称性(SIA)和Rashba自旋劈裂. 本文研究了Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中第一子带的Rashba 系数和Rashba自旋劈裂随Al_0.3Ga_0.7N插入层(右阱)的厚度w_s以及外加电场的变化关系, 其中GaN层(左阱)的厚度为40-w_s Å. 发现随着w_s的增加, 第一子带的Rashba系数和Rashba自旋劈裂首先增加, 然后在w_s>20 Å 时它们迅速减小, 但是w_s>30 Å时Rashba自旋劈裂减小得更快, 因为此时k_f也迅速减小. 阱层对Rashba系数的贡献最大, 界面的贡献次之且随w_s变化不是太明显, 垒层的贡献相对比较小. 然后, 我们假w_s=20 Å, 发现外加电场可以很大程度上调制该体系的Rashba系数和Rashba自旋劈裂, 当外加电场的方向同极化电场方向相同(相反)时, 它们随着外加电场的增加而增加(减小). 当外加电场从-1.5×10⁸ V·m^-1到1.5×10⁸ V· m^-1变化时, Rashba系数随着外加电场的改变而近似线性变化, Rashba自旋劈裂先增加得很快, 然后近似线性增加, 最后缓慢增加. 研究结果表明可以通过改变GaN层和Al_0.3Ga_0.7N层的相对厚度以及外加电场来调节Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中的Rashba 系数和Rashba自旋劈裂, 这对于设计自旋电子学器件有些启示.     

Theoretical study of miniature optically pumped cavity NH3 Far-infrared laser

Miniature optically pumped cavity NH3 Far-infrared laser was studied theoretically, with the length of the FIRL cavity as short as 1.5cm, the dependences of FIRL output power and laser lineshape on operating gas pressure and output coupling condition, and on the effect of laser line saturation broadening were calculated.Supported by the National Natural Science Foundation of China.     

Studies on the preparation and ethanol gas sensing properties of spinel Zn0.6Mn0.4Fe2O4 nanomaterials

Zn_1−xMn_xFe₂O₄ (x = 0, 0.2 and 0.4) nanomaterials were synthesized by sol–gel citrate method and studied structural and gas sensing properties. The structural characteristics of synthesized nanomaterials were studied by X-ray diffraction measurement (XRD) and transmission electron microscope (TEM). The results revealed that the particle size is in the range of 30–35 nm for Mn–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like LPG, CH_4, CO and ethanol and it is observed that Mn–Zn ferrite shows high response to ethanol at relatively lower operating temperature. The Zn_0.6Mn_0.4Fe₂O₄ nanomaterial shows better sensitivity towards ethanol at an operating temperature 300 °C. Incorporation of 1.5 wt.% Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 °C to 230 °C for ethanol sensor. The response time of 200 ppm ethanol in air is about 10s.     

Photoluminescence enhancement by localized surface plasmons in AlGaN/GaN/AlGaN double heterostructures

Double heterostructures AlGaN/GaN/AlGaN grown by hydride vapor phase epitaxy and designed for use as light emitting diodes for 360 nm wavelength were patterned by shallow nanoholes and injected with Ag/SiO₂ or Al nanoparticles. A 1.8 times increase in the photoluminescence and microcathodoluminescence signal from the GaN active region was observed for 100 nm diameter Al nanoparticles, the efficiency decreased compared to the reference planar samples for small Al nanoparticles of 30–40 nm diameter, and a moderate increase of 1.2 times was detected for Ag/SiO₂ nanoparticles. The observed phenomena are explained by the GaN emitter coupling with localized surface plasmons produced by metallic nanoparticles. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

TiO2微粒对远程荧光粉膜及白光发光二极管器件光色性能的影响

利用热压法将TiO₂微粒掺入至YAG:Ce荧光粉和硅树脂中制备出远程荧光粉膜并封装成白光发光二极管(LED)器件, 通过荧光粉相对亮度仪、双积分球测试系统和可见光光谱分析系统对样品的光色性能及机理进行了研究. 结果表明: TiO₂的散射效应能够显著提高蓝光的利用率和黄光的透射强度, 白光LED器件的光通量在TiO₂浓度为0.966 g/cm³ 时达到最高值415.28 lm(@300 mA, 9.3 V), 提高了8.15%, 相关色温从冷白6900 K逐渐变化至暖白3832 K. TiO₂的掺入不仅提高了远程荧光粉膜的发射强度和白光LED器件的光通量, 同时能调控其相关色温.     

利用单层密排的纳米球提高发光二极管的出光效率

在发光二极管(LED)的透明电极层上制作单层六角密排的聚苯乙烯(polystyrene, PS) 纳米球, 研究提高GaN基蓝光LED的出光效率. 采用自组装的方法在透明电极铟锡氧化物层上制备了直径分别约为250, 300, 450, 600和950 nm的PS纳米球, 并且开展了电致发光的研究. 结果表明, 在LED的透明电极层上附有PS纳米球能有效地提高LED的出光效率; 当PS纳米球的直径与出射光的波长比较接近时, LED的出光效率最优. 与参考样品相比, 在20 mA和150 mA工作电流下, 附有PS纳米球的样品的发光效率分别增加1.34倍和1.25倍. 三维时域有限差分方法计算表明, 该出光增强主要归因于附有PS纳米球的LED结构可以增大LED结构的光输出临界角, 从而提高LED的出光效率. 因此, 这是一种低成本的实现高效率LED的方法.     

Magnetoresistance and magnetostriction of Co2Cr0.6Fe0.4Al Heusler alloy

We report a study of the magnetotransport properties of the Co₂Cr_0.6Fe_0.4Al Heusler alloy grown by means of the arc-melting technique. X-ray diffraction and energy dispersive X-ray spectroscopy have been used to analyze the crystallographic structure and the sample stoichiometry. Temperature-dependent magnetization measurements have been carried out in the range 300-850 K. Co₂Cr_0.6Fe_0.4Al is theoretically predicted to have full positive spin polarization at the Fermi level, and as a consequence its spin-dependent transport properties are being intensively studied. Low field magnetoresistance exceeding 30% has been observed very recently in Co₂Cr_0.6Fe_0.4Al compact pellets. We have performed magnetoresistance and magnetostriction measurements in both the as-grown alloy and compact pellets made of mechanically milled Co₂Cr_0.6Fe_0.4Al. The as-grown and the milled sample show negligible anisotropic magnetostriction (25 μst at saturation), whilst only the milled sample exhibits magnetoresistance (0.65% at 300 K). These results permit us to discard the magnetostrictive effects as the magnetoresistance source.