MOCVD两步生长法制备GaN量子点

报道了用金属有机化学气相沉积方法在蓝宝石衬底上成功地制备出ＧａＮ量子点。     

碳纳米管电磁量子性质的研究

对碳纳米管电磁特性的研究进展进行了系统的综述,并溶入我们最近对碳纳米管输运特性、本征电阻、磁阻等的研究结果,简洁地介绍了碳纳米管电磁量子特性研究的方法、理论、主要发现及意义.     

Au量子点I－V特性的计算机模拟

基于量子力学隧穿原理，对由Au纳米粒子自组装体系构建的典型串联双隧道结模型的I－V特性进行了计算机模拟，模拟结果与实验曲线吻合。该方法对于构建纳米电子器件模型及工艺优化将具有指导意义。     

极化效应对AIN／GaN共振隧穿二极管电流特性的影响

本文采用半经验紧束缚能带理论，通过自洽计算薛定谔方程和泊松方程研究了A1N／GaN共振隧穿二极管中极化效应对电流的影响。结果发现，极化效应导致电流曲线发生不对称性，并影响电流的共振电压位置，这与实验报道的结果相一致。并且随着极化电荷的增加，在一定的偏压条件下，只能观测到一个子能级隧穿或者根本没有负微分电阻现象发生。     

CdS量子点的制备和光学性质

以醋酸镉、硫粉为原料制备CdS量子点,研究了硫的加入量对其光学性质的影响,结果表明:合成的CdS量子点粒径均匀,分散性较好,随着硫加入量的增加CdS量子点的粒径增大;反应中过量的硫能有效地填补硫空位,从而抑制表面态发光,同时,ODA的修饰也能有效地钝化表面态,减小表面态的发光强度.     

碳量子点的一步合成及其发光性质的研究

本文采用油浴加热柠檬酸一步法合成碳量子点,用HRTEM透射电镜和FTIR红外光谱对其形貌和结构进行表征。研究该碳量子点的荧光性质,初步探讨了其发光的可能机理。实验结果表明,该方法合成的碳量子点粒径大小为3~5 nm,在360 nm处有一个很强的紫外吸收峰,最大激发波长和发射波长分别为365 nm和460 nm,其光学稳定性良好,在pH5.0~7.0范围内,碳量子点的荧光强度随pH的变化比较敏感。     

退火条件对Sn量子点生长和红外光学性质的影响

首次采用固相外延生长技术在Si(001)表面直接生长Sn量子点,并应用原子力显微镜(AFM)、X射线衍射(XRD)和同步辐射傅里叶红外光谱(FTIR)研究了退火条件对量子点样品的表面形貌、结晶性和红外光学性质的影响.AFM结果表明,随着退火温度的升高和退火时间的延长,量子点的平均尺寸变大,面密度减小.XRD结果显示,外延得到的Sn量子点为四方结构的β-Sn,与衬底的相对取向为Sn(110)//Si(001).由于β-Sn量子点的尺寸仍较大,同步辐射FTIR谱中没有观察到量子点的特征吸收峰.     

量子点激光器的研究

总结量子点激光器的基本原理与制备方法及量子点激光器的基本结构和性能,最后阐述量子点激光器的研究进展,并展望量子点激光器的应用前景及必须解决的问题。     

结构对称性对双量子点干涉仪中量子输运的影响

采用非平衡格林函数方法求解量子输运过程,探讨结构对称性对双量子点干涉仪中量子输运的影响,结果表明,调节点一导线间耦合,导致双量子点干涉仪结构对称性和电子传输路径不同,使得电子隧穿并联双量子点结构呈现出一系列的新奇特性。当点一导线间的耦合强度不同,两量子点中阶梯状的平均电子占据数的分离程度不同,且两台阶的平缓程度也不同,证明了结构决定性能,也为设计可控量子器件提供一个理论依据。     

含氮石墨烯量子点的制备及其光学性质研究

采用水热法一步合成了含氮石墨烯量子点(NGQDs), 通过原子力显微镜(AFM)、透射电镜(TEM)、X射线光电子能谱(XPS)等对NGQDs的形貌和组成进行表征, 并进一步通过紫外-可见光谱(UV-Vis)、荧光光谱(PL)等手段研究了NGQDs的光学性质。AFM和TEM分析结果表明, NGQDs尺寸约为8.9 nm、厚度为0.6 ~2.0 nm (即1~3个碳原子层)。XPS分析结果表明NGQDs中氮含量约为17%, 且氮元素主要以“吡咯N”形式存在。光谱学实验表明, NGQDs的激发光谱与吸收光谱基本一致, 且其发射光谱与激发波长之间不存在依赖关系。此外, NGQDs的量子产率为~18%, 并随着含氮量的增加而增加, 且其荧光寿命衰变曲线可以被拟合成很好的双指数衰变曲线(τ₁=2.93 ns, τ₂=9.00 ns), 表明NGQDs有两种发色源, 即边缘富有含氧官能团的sp²碳簇和含氮五元环-吡咯环。     

MBE grown InGaN quantum dots and quantum wells: effects of in-plane localization

InGaN/GaN heterostructure samples were grown by molecular beam epitaxy using ammonia as a nitrogen precursor. The growth of InGaN/GaN self-assembled quantum dots was monitored in situ by reflection high energy electron diffraction intensity oscillations. Atomic force microscopy scans showed a very high density of InGaN islands, 1×10¹¹ cm⁻², well above the dislocation density. This could explain the increased radiative efficiency of these samples compared to homogeneous quantum wells. Light emitting diodes (LEDs) with InGaN active layers buried in GaN were realized. Electroluminescence and photocurrent spectra of these LEDs evidence a strong Stokes shift that can be attributed to high localization of carriers in InGaN layers.     

Investigation of V-defects formation in InGaN/GaN multiple quantum well grown on sapphire

In the growth of InGaN multiple quantum well structure, V-pits has been observed to be initiated at the threading dislocations which propagate to the quantum well layers with high indium composition and substantially thick InGaN well. A set of samples with varying indium well thickness (3-7.6 nm) and composition (10-30%) are grown and characterized by photoluminescence (PL), X-ray diffraction, transmission electron microscopy and atomic force microscopy. The indium content and the layer thicknesses in InGaN/GaN quantum well are determined by high-resolution X-ray diffraction (XRD) and TEM imaging. With indium composition exceeding 10%, strain at the InGaN/GaN interface leads to the generation of V-pits at the interlayers of the MQW. Higher indium composition and increase in thickness of a period (InGaN well plus the GaN barrier) appear to enhance pits generation. With thicker InGaN well and reduction in thickness of GaN to InGaN (or the R ratio), pit density is substantially reduced, but it results in greater inhomogeneity in the distribution of indium in the InGaN well. This leads to a broadened PL emission and affect the PL emission intensity.     

Growth of InGaN quantum dots with AlGaN barrier layers via modified droplet epitaxy

The growth of c-plane InGaN quantum dots via modified droplet epitaxy with AlGaN barrier layers is reported. The growth of the AlGaN layer underlying the InGaN quantum dot layer was carried out under H₂ at 1050 °C, while the capping AlGaN layer was grown at the same temperature (710 °C) and using the same carrier gas (N₂) as that used to grow the InGaN quantum dot layer to prevent decomposition of the InGaN. Atomic force microscopy of InGaN epilayers grown and annealed on high temperature AlGaN using identical growth conditions used for the quantum dot samples highlighted a narrower distribution of nanostructure heights than that obtained for similar growth on GaN. Scanning transmission electron microscopy (STEM) imaging combined with energy dispersive X-ray (EDX) analysis revealed the presence of a thin high aluminium content layer at the surface of both AlGaN layers, which is believed to be related to loss of Ga during temperature ramping processes. Micro-photoluminescence studies carried out at low temperature revealed near resolution-limited peaks while time-resolved measurements on these peaks demonstrated mono-exponential decay times between 1 and 4 ns, showing that quantum dots had successfully been formed between the AlGaN barriers. Temperature-dependant measurement of the emission lines revealed that quenching of the peak often occurred at ∼60–70 K, with some of the peaks exhibiting significant line broadening whilst others remained narrow.     

Investigations of selectively grown GaN/InGaN epitaxial layers

We have studied GaN/InGaN heterostructures grown by selective area low pressure metalorganic vapor phase epitaxy (LP-MOVPE). A GaN layer already grown on the c-face of sapphire has been used as substrate, partly masked by SiO₂. In a second epitaxial step a GaN/InGaN single heterostructure and GaN/InGaN/GaN double heterostructures were grown on the unmasked rectangular fields. We obtained good selectivity for GaN and for InGaN. A larger growth rate as compared to planar epitaxy and strong growth enhancement at the edges was observed. Spatially resolved measurements of the luminescence show an increase in indium incorporation of about 80% at the edges. Besides the larger indium offering at the edges, this is due to an enhanced growth rate. Very smooth facets are obtained. The influence of pressure on the surface morphology and growth enhancement was investigated.     

2D/3D growth of GaN by molecular beam epitaxy: towards GaN quantum dots

The first stages of the growth of strained GaN on AlN were studied using reflection high energy electron diffraction, atomic force microscopy and high resolution electron microscopy. It was shown that GaN grows in the Stranski–Krastanov mode, with three-dimensional islanding occuring after deposition of two monolayers. This 2D/3D transition was found to depend on the growth temperature. At low growth temperature, coalescence of 3D islands rapidly leads to a smooth surface. At high temperature, no smoothing process is observed. It is shown that the size of the 3D islands is controlable and that it is small enough to expect quantum effects.     

Synthesis and characterization of CdTe quantum dots embedded gelatin nanoparticles via a two-step desolvation method

Novel CdTe quantum dots (QDs) embedded gelatin nanoparticles (CdTe/gelatin nanoparticles) were synthesized via a two-step desolvation method. The morphology and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and laser particle size analyzer. They are presented spherically and relatively uniform with a diameter of 150 nm. The luminescent properties of the nanoparticles were investigated by using fluorescence spectrophotometry and fluorescence microscopy. The fluorescence stability of nanoparticles was tested in vitro. It was found that the nanoparticles were stable in water and phosphate-buffered saline (PBS) solution (pH 7.4) for at least 15 days. A possible formation mechanism of the CdTe/gelatin nanoparticles was also proposed. The inherent stability and biocompatibility indicate that the nanoparticles are expected to be promising candidates for in vivo biological imaging studies.     

Thermal effect of multi-quantum barriers within InGaN/GaN multi-quantum well light-emitting diodes

We introduce the InGaN/GaN multi-quantum barriers (MQBs) into InGaN/GaN multi-quantum well (MQW) heterostructures to improve the performance of light-emitting diodes. The temperature and injection current dependent electroluminescence were carried out to study the thermal effect of InGaN/GaN MQWs. We observe the enhancement of carrier confinement in the active layer and the inhibited carrier leakage over the barrier for the sample with MQBs. In addition, the external quantum efficiency of the samples is obtained. It is found that the radiative efficiency of the sample possessing MQBs exhibits less sensitive temperature dependence and leads to an improved efficiency in the high temperature and high injection current range.     

Recombination dynamics of localized excitons in self-formed InGaN quantum dots

The dynamic behavior of radiative recombination has been assessed in the InGaN-based purple, blue and green light emitting diodes (LEDs), as well as in purple laser diode (LD) components by means of time-resolved electroluminescence (TREL) and time-resolved photoluminescence (TRPL) spectroscopy. It was found that excitons localized at deep trap centers play an important role in the recombination process. Microstructural analysis suggests that these centers originate from the In-rich regions, acting as quantum dots which are self-formed within the wells. The radiative lifetime of localized excitons in the LD structure was almost constant at 6 ns in the temperature range between 20 and 200 K, indicating the zero-dimensional feature of excitons.