Temperature Dependence of Emission Properties of Self-Assembled InGaN Quantum Dots

Emission properties of self-assembled green-emitting InGaN quantum dots （QDs） grown on sapphire substrates by using metal organic chemical vapor deposition are studied by temperature-dependent photoluminescence （PL） measurements. As temperature increases （15-300K）, the PL peak energy shows an anomalous V-shaped （redshift blueshift） variation instead of an S-shaped （redshift-blueshift-redshift） variation, as observed typically in green-emitting InGaN/GaN multi-quantum wells （MOWs）. The PL full width at half maximum （FWHM） also shows a V-shaped （decrease-increase） variation. The temperature dependence of the PL peak energy and FWHM of QDs are well explained by a model similar to MOWs, in which carriers transferring in localized states play an important role, while the confinement energy of localized states in the QDs is significantly larger than that in MOWs. By analyzing the integrated PL intensity, the larger confinement energy of localized states in the QDs is estimated to be 105.9meV, which is well explained by taking into account the band-gap shrinkage and carrier thermalization with temperature. It is also found that the nonradiative combination centers in QD samples are much less than those in QW samples with the same In content.     

络合滴定法测定硅铁中铝含量的改进

络合滴定法测定硅铁中铝量,GB4333.5—84中用甲基异丁基酮将铁萃取后,用硫酸铜标准溶液滴定过量的EDTA,加入氟化钠释放与铝络合的EDTA,再用硫酸铜标准溶液回滴,由于该法操作条件严格,费时,不能适用于一般中小企业生产控制要求.本文在试样以硝酸、氢氟酸溶解,高氨酸冒烟驱除氟后,采用氢氧化钠一氯化钠体系沉淀Fe(Ⅲ),过滤后加入过量EDTA,在pH 5.5条件下,用硫酸铜标准溶液滴定过量的EDTA,获得了令人满意的结果.1 主要试剂与仪器吡啶基偶氮萘酚(PAN)乙醇溶液:2g·L~(-1)乙酸-乙酸钠缓冲溶液:PH 5.5混合液:50g·L~(-1)氯化钠与10g·L~(-1)氢氧化钠溶液按1:1混合.对硝基酚乙醇溶液:2g·L~(-1)EDTA标准溶液:0.02mol·L~(-1),称取基准乙     

光电耦合对InGaN/GaN量子阱光学性能的影响

围绕高性能GaN基垂直腔面发射激光器(VCSELs),设计了两种具有不同光电耦合强度的InGaN/GaN量子阱(QWs)样品,研究了它们的光学性质。样品A在腔模的两个波腹处各放置两个InGaN耦合量子阱,而样品B在腔模的一个波腹处放置5个InGaN耦合量子阱。计算表明样品A具有较大的相对光限制因子1.79,而样品B为1.47。光学测试发现样品A有着更高的内量子效率(IQE)和更高的辐射复合效率。使用两种样品制作了光泵VCSEL结构,在光激发下实现激射,其中基于样品A的VCSEL有着更低的激射阈值。结果表明有源区结构会显著影响量子阱与光场的耦合作用、外延片的内量子效率、辐射复合寿命和VCSEL激射阈值,同时也说明样品A的有源区结构更有利于制作低阈值的VCSEL器件。     

醚链桥接芳香二醛及其缩氨硫脲的合成

一些缩氨硫脲及其衍生物对结核、麻风、风湿、疟疾、天花、真菌和某些肿瘤有一定的药理活性。缩氨硫脲的真菌活性是由于它的配位原子在生物体的新陈代谢中和真菌所需的金属离子螯合。缩氨硫脲具有与氨基酸、肽、蛋白质、酶、核糖核酸等生物配体相同的配位原子、被看作研究生物配体和痕量金属离子配位的优良模型。因为聚乙二醇醚链上的氧原子能与金属离子配位,所以在缩氨硫脲分子中连接上聚乙二醇醚链,增加缩氨硫脲分子中的配位原子种类和数目,也许能够增强螯合剂的配位能力,扩展其与金属离子的螯合围范。为此,我们将缩乙二醇二氯化物和苯环上带酰基的苯酚反应,制成化合物1_(a-h),然后再与硫代氨基脲缩合,得到醚链桥接的芳香醛缩氨硫脲2_(a-g)。它们的合成路线和主要结构如下:     

聚乙二醇醚链桥接缩氨脲和缩甲硫基氨基硫脲的合成

一些缩氨硫脲对结核,麻风、风湿、疟疾、天花、真菌和肿瘤有一定的药理活性。考虑到变更缩氨硫脲的硫代羰基上的硫原子为氧原子,或者变更其端基有可能改变其药理活性,在前文基础上,本文继续报道聚乙二醇醚链桥接缩氨硫脲和缩甲硫基氨基硫脲的合成。以缩二醇二氯化物合产物与甲酰基苯酚的缩合产物再与相应的氨基脲和甲硫基氨基硫脲反应,制得化合物1-8。     

Silica-based microcavity fabricated by wet etching

Silica whispering gallery mode(WGM) microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10~4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.     

氮化物垂直腔面发射激光器的发展与挑战(特邀)

垂直腔面发射激光器凭借阈值低、发散角小、调制速率高以及输出光束呈圆斑对称等特点,迅速成为当下半导体激光器的研究热点.氮化镓(GaN)材料是制造紫外到绿光波段光电子器件的理想材料,经过四十余年的研究,蓝光和绿光LED在照明、显示等领域得到广泛应用.技术含量更高的激光器件也已进入了应用的快车道,即将覆盖照明、通信、投影显示...     

GaN基白光发光二极管失效机理分析

对小功率白光GaN基发光二极管(LED)在室温、40 ℃和70 ℃下进行温度加速老化寿命实验,通过对老化前后不同时间段器件的电学、光学和热学特性进行测量来分析器件的失效机理,着重分析器件的芯片和荧光粉的失效机理.器件老化前后的I-V特性表明:老化过程中,器件的串联电阻和低正向偏压下的隧道电流增大,这是由于器件工作时其芯片的欧姆接触退化和半导体材料的缺陷密度升高而引起的.器件的热特性表明:高温度应力下器件的热阻迅速变大,封装材料迅速退化,这是器件退化的主要原因;光谱曲线表明温度加速了器件的     

The exciton-longitudinal-optical-phonon coupling in InGaN/GaN single quantum wells with various cap layer thicknesses

This paper studies the exciton-longitudinal-optical-phonon coupling in InGaN/GaN single quantum wells with various cap layer thicknesses by low temperature photoluminescence (PL) measurements.With increasing cap layer thickness,the PL peak energy shifts to lower energy and the coupling strength between the exciton and longitudinal-optical (LO) phonon,described by Huang-Rhys factor,increases remarkably due to an enhancement of the internal electric field.With increasing excitation intensity,the zero-phonon peak shows a blueshift and the Huang-Rhys factor decreases.These results reveal that there is a large built-in electric field in the well layer and the exciton-LO-phonon coupling is strongly affected by the thickness of the cap layer.