氮化镓基发光二极管产业化中的材料物理问题

第三代半导体氮化镓化合物半导体已成为蓝光发光二极管的主流材料，国际上的产业化已成规模，国内也有多家处于中试阶段，由于氮化镓基材料中有如此多的问题没有解决，材料制备设备，器件工艺也极需改进及优化，这既给了中国科研人员及工程技术人员一个机遇，也使他们面临着严峻的挑战。     

具有超晶格应力调制结构的绿光InGaN/GaN多量子阱的发光特性

研究了具有InGaN/GaN超晶格(SL)插入结构的绿光InGaN/GaN多量子阱(MQW)的发光特性。结构测试表明,SL插入结构并没有引起MQW中平均In组份的增加,而是改变了In组份的分布,形成了高In组份的量子点和低In组份量子阱。其电致发光(EL)谱和光致发光(PL)谱均出现了双发光峰。我们认为这两个 峰分别来自于量子点和量子阱,且存在着载流子从阱向点转移的输运机制。最后变温PL积分强度的Arrhenius 拟合表明,SL插入结构并没有在MQW中引入新的缺陷,使其发光效率下降。     

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.     

一种简单高效的制备硅纳米孔阵结构的方法

本文介绍了一种简单高效的制备硅纳米孔阵结构的方法. 利用激光干涉光刻技术, 结合干法和湿法刻蚀工艺, 直接将光刻胶点阵刻蚀为硅纳米孔阵结构, 省去了图形反转工艺中的金属蒸镀和光刻胶剥离等必要步骤, 在2英寸的硅 (001) 衬底上制备了高度有序的二维纳米孔阵结构. 利用干法刻蚀产生的氟碳有机聚合物作为湿法刻蚀的掩膜, 以及在干法刻蚀时对样品进行轻微的过刻蚀, 使SiO₂点阵图形下形成一层很薄的硅台面, 是本方法的两个关键工艺步骤. 扫描电子显微镜图片结果表明制备的孔阵图形大小均匀, 尺寸可控, 孔阵周期为450 nm, 方孔大小为200–280 nm. 关键词： 激光干涉光刻 纳米阵列 刻蚀 氟碳有机聚合物     

Growth of Semi-Insulating GaN by Using Two-Step AIN Buffer Layer

Semi-insulating GaN is grown by using a two-step A1N buffer layer by metalorganic chemical vapour deposition. The sheet resistance of as-grown semi-insulating GaN is dramatically increased to 10^13 Ω/sq by using two-step A1N buffer instead of the traditional low-temperature GaN buffer. The high sheet resistance of as-grown GaN over 10^13 Ω/sq is due to inserting an insulating buffer layer （two-step A1N buffer） between the high-temperature GaN layer and a sapphire substrate which blocks diffusion of oxygen and overcomes the weakness of generating high density carrier near interface of GaN and sapphire when a low-temperature GaN buffer is used. The result suggests that the high conductive feature of unintentionally doped GaN is mainly contributed from the highly conductive channel near interface between GaN and the sapphire substrate, which is indirectly manifested by room-temperature photoluminescence excited by an incident laser beam radiating on growth surface and on the substrate. The functions of the two-step A1N buffer layer in reducing screw dislocation and improving crystal quality of GaN are also discussed.     

Room-temperature operating extended short wavelength infrared photodetector based on interband transition of InAsSb/GaSb quantum well

Here in this paper,we report a room-temperature operating infrared photodetector based on the interband transition of an In As Sb/Ga Sb quantum well.The interband transition energy of 5-nm thick In As_(0.91)Sb_(0.09) embedded in the Ga Sb barrier is calculated to be 0.53 e V(2.35μm),which makes the absorption range of In As Sb cover an entire range from short-wavelength infrared to long-wavelength infrared spectrum.The fabricated photodetector exhibits a narrow response range from 2.0μm to 2.3μm with a peak around 2.1μm at 300 K.The peak responsivity is 0.4 A/W under-500-m Vapplied bias voltage,corresponding to a peak quantum efficiency of 23.8%in the case without any anti-reflection coating.At 300 K,the photodetector exhibits a dark current density of 6.05×10~(-3)A/cm~2under-400-m V applied bias voltage and3.25×10~(-5)A/cm~2under zero,separately.The peak detectivity is 6.91×10~(10)cm·Hz~(1/2)/W under zero bias voltage at 300 K.     

Luminescent Characteristics of Near Ultraviolet InGaN/GaN MQWs Grown on Grooved Sapphire Substrates Fabricated by Wet Chemical Etching

InGaN/GaN multiple quantum wells （MQWs） are grown on planar and maskless periodically grooved sapphires by metal organic vapour phase epitaxy （MOCVD）. High-resolution x-ray rocking curves and transmission electron microscopy （TEM） are adopted to characterize the film quality. Compared with the MQWs grown on planar sapphire, the sample grown on grooved sapphire shows better crystalline quality： a remarkable reduction of dislocation densities is achieved. Meanwhile, the MQWs grown on grooved sapphire show two times larger PL intensity at room temperature. Temperature-dependent PL measurements are adopted to investigate the luminescence properties. The luminescence thermal quenching based on a fit to the Arrhenius plot of the normalized integrated PL intensity over the measured temperature range suggests that the nonradiative recombination centres （NRCs） are greatly reduced for the sample grown on grooved sapphire. We assume that the reduction of dislocations which act as NRCs is the main reason for the sample grown on pattern sapphire having higher PL intensity.     

Growth and Characteristics of Epitaxial AlxGa1-xN by MOCVD1

AlxGa1-xN epilayers with a wide Al composition range （0.2 ≤ x ≤0.68） were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapour deposition （LP-MOCVD）. X-ray diffraction results reveal that both the （0002） and （1015） full widths at half-maximum （FWHM） of the AlxGa1-xN epilayer decrease with increasing Al composition due to the smaller lattice mismatch to the AlN template. However, the surface morphology becomes rougher with increasing Al composition due to the weak migration ability of Al atoms. Low temperature photolumineseence （PL） spectra show pronounced near band edge （NBE） emission and the NBE FWHM becomes broader with increasing Al composition mainly caused by alloy disorder. Meanwhile, possible causes of the low energy peaks in the PL spectra are discussed.     

纳米结构的制备及单电子器件研究

建立了单电子器件的制备工艺和单电子器件的分析、测量系统,研究了有潜在应用价值的纳米结构加工技术,制备了适合光电集成的多种纳米结构,发展了常规光刻法制备单电子器件的多种技术,其中,在生命科学和信息领域有着广泛应用的“纳米电极对”引起了国内外专家的重视,发展以“纳米电极对”为基础的单电子器件及其应用是我们目前的主要研究方向,目前我们正在探索这种单电子器件在生命芯片、微电子系统集成方面的应用。     

Three-Step Growth Optimization of AlN Epilayers by MOCVD

A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.