液液相变中的盐效应

完全互溶的双液系在一定条件下发生相变而成为部分互溶体系.六十年代,李俊甫等曾研究过盐的加入对相变条件的影响,提出了线性方程:T=T_0+Kx_x。(T_0,T分别为双液比固定时加盐前后体系的相变温度,x_s为盐的摩尔分数,K为常数).但至今尚无人从理论上证明其存在并加以计算.本文试从微扰理论出发证明该线性方程成立,并对部分体系进行计算。     

Simulation of the light extraction efficiency of nanostructure light-emitting diodes

The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar,nanorough of P-GaN surface,coreshell and nano-interlayer structure.From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures,especially those with an InGaN or AlGaN nano-interlayer.With a 420-nm luminescence wavelength,the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.     

Different variation behaviors of resistivity for high-temperature-grown and low-temperature-grown p-GaN films

Two series of p-GaN films grown at different temperatures are obtained by metal organic chemical vapor deposition(MOCVD). And the different variation behaviors of resistivity with growth condition for high- temperature(HT)-grown and low-temperature(LT)-grown p-GaN films are investigated. It is found that the resistivity of HT-grown p-GaN film is nearly unchanged when the NH_3 flow rate or reactor pressure increases. However, it decreases largely for LT-grown p-GaN film.These different variations may be attributed to the fact that carbon impurities are easy to incorporate into p-GaN film when the growth temperature is low. It results in a relatively high carbon concentration in LT-grown p-GaN film compared with HT-grown one. Therefore, carbon concentration is more sensitive to the growth condition in these samples, ultimately,leading to the different variation behaviors of resistivity for HT- and LT-grown ones.     

Output light power of InGaN-based violet laser diodes improved by using a u-InGaN/GaN/AlGaN multiple upper waveguide

The upper waveguide(UWG) has direct influences on the optical and electrical characteristics of the violet laser diode(LD) by changing the optical field distribution or barrier of the electron blocking layer(EBL). In this study, a series of In GaN-based violet LDs with different UWGs are investigated systematically with LASTIP software. It is found that the output light power(OLP) under an injecting current of 120 mA or the threshold current(Ith) is deteriorated when the UWG is u-In_(0.02)Ga_(0.98)N/GaN or u-In_(0.02)Ga_(0.98)N/Al_xGa_(1-x)N(0 ≤ x ≤ 0.1), which should be attributed to small optical confinement factor(OCF) or severe electron leakage. Therefore, a new violet LD structure with u-In_(0.02)Ga_(0.98)N/GaN/Al_(0.05)Ga_(0.95)N multiple layer UWG is proposed to reduce the optical loss and increase the barrier of EBL. Finally,the output light power under an injecting current of 120 mA is improved to 176.4 mW.     

直觉模糊GM(1,1)模型及其在灰色发展决策的应用

研究了以直觉模糊数为对象的GM(1,1)模型并运用到灰色发展决策方法。利用灰色系统理论中核和灰度的内涵,将直觉模糊数的犹豫度和记分函数结合构建了直觉模糊数序列 GM(1,1)预测模型,从而实现了直觉模糊数的预测。在此基础上结合变权原理提出了基于直觉模糊数的灰色发展决策方法。最后,算例分析说明了该方法的合理性和可行性。     

Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters,such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition,using an in-plane grazing incidence x-ray diffraction technique.The results are analysed and compared with a complementary out-of-plane xray diffraction technique.The twist of the GaN mosaic structure is determined through the direct grazing incidence measurement of (100) reflection which agrees well with the result obtained by extrapolation method.The method for directly determining the in-plane lattice parameters of the GaN layers is also presented.Combined with the biaxial strain model,it derives the lattice parameters corresponding to fully relaxed GaN films.The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established,reaching to a maximum level of-0.89 GPa.     

Time delay in InGaN multiple quantum well laser diodes at room temperature

This paper reports that a long delay between the beginning of pumping current pulse and the onset of optical pulse is observed in InGaN laser diodes.The delay time decreases as the pumping current increases,and the speed of the delay time reduction becomes slower as the current amplitude increases further.Such delay phenomena are remarkably less serious in laser diodes grown on GaN substrate than those on sapphire.It attributes the delay to the traps which cause a large optical loss by saturable absorption and retard the laser action.The traps can be bleached by capturing injected carriers.The effect of GaAs laser irradiation on InGaN laser action demonstrates that the traps responsible for the delay are deep centres which can be filled by the photo-assisted processes.     

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.     

含盐体系的静态介电常数

应用剩余极化的概念和Mori布朗运动方程,得介电常数的计算公式。应用于H₂O-LiCl、H₂O-NaCl、CH₃OH-LiCl,CH₃OH-NaCl、CH₃OH-Nal、HCONH₂-NaI表明,水盐体系的计算值接近实验值,HCONH₂-NaI较差。     

考虑双参照点和Choquet积分的新型研发机构绩效评估方法及应用

针对新型研发机构绩效评估值不确定、指标间存在关联、投资主体多元且有风险偏好、指标集权重未知等绩效问题,提出基于双参照点和Choquet积分的绩效评估方法。首先,结合新型研发机构的特点,构建绩效评估指标体系;其次,基于累积前景理论设计同行-期望双参照点;然后,构建指标间直接关联矩阵,依据K-可加模糊测度和平均边际贡献Banzhaf值优化求解指标集权重,代入Choquet积分方法和参照点权重公式计算各新型研发机构的综合绩效评估值,从而实现机构排序和问题分析。该方法考虑了新型研发机构的特点、数据不确定性、指标关联性、风险偏好性、权重未知性等因素,更加符合实际情况,案例验证了方法的有效性和实用性。