大功率短波长InAlGaAs/AlGaAs量子点超辐射发光管

为了满足超辐射发光管的短波长应用,采用InAlGaAs/AlGaAs量子点有源区和干法刻蚀工艺制备了短波长弯曲波导超辐射发光管。在1.6A脉冲电流注入下,器件峰值输出功率为29mW,中心波长为880nm,光谱半高宽为20.3nm。比较了干法刻蚀工艺和湿法腐蚀工艺对超辐射发光管器件性能的影响。在1.6A脉冲电流注入下,湿法腐蚀制备的器件峰值输出功率仅为7mW。与湿法腐蚀相比,干法刻蚀可以精确控制波导形状和参数,降低波导损耗,有效增大器件输出功率。     

InAs/GaAs submonolayer quantum dot superluminescent diode emitting around 970 nm

According to the InAs/GaAs submonolayer quantum dot active region, we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm. At a pulsed injection current of 0.5 A, the device exhibits an output power of 24 mW and an emission spectrum centred at 971 nm with a full width at half maximum of 16 nm.     

InAs/GaAs submonolayer quantum-dot superluminescent diodes with active multimode interferometer configuration

With a chirped InAs/GaAs SML-QD (quantum dot) structure serving as the active region, the superluminescent diodes emitting at wavelength of around 970nm are fabricated. By using an active multimode interferometer configuration, these devices exhibit high continue-wave output powers from the narrow ridge waveguides. At continue-wave injection current of 800mA, an output power of 18.5mW, and the single Gaussian-like emission spectrum centered at 972nm with a full width at half maximum of 18nm are obtained.     

垂直结构多色量子点LED(QD-LED)最新进展

量子点LED以胶体量子点为发光层,通过调节作为发光层量子点的尺寸可以制作出覆盖可见(380-780nm)以及近红外光谱的量子点LED(QD-LED),而且量子点LED器件发出的光谱范围很窄,其光谱半高宽可达30nm。简述了当今国内外关于QD-LED器件结构的研究成果以及器件的制作工艺,介绍了目前课题组最新的一些相关成果。重点阐述了目前已经得到验证的几种量子点器件结构,分析了其存在的优缺点,这些结论对进一步改进QD-LED的结构以及使其可以更有利于商业化提供了参考。     

含有AlGaAs插入层的InAs/GaAs三色量子点红外探测器

本文报道了采用分子束外延技术制备的三色InAs/GaAs量子点红外探测器. 器件采用nin型结构, 吸收区结构是在InGaAs量子阱中生长含有AlGaAs插入层的InAs量子点, 器件在77 K下的红外光电流谱有三个峰值: 6.3, 10.2和11 μm. 文中分析了它们的跃迁机制, 并且分别进行了指认. 因为有源区采用了不对称结构, 所以器件在外加偏压正负方向不同时, 光电流谱峰值的强度存在一些差异. 不论在正偏压或者负偏压下, 当偏压达到较高值, 再进一步增大偏压时, 都出现了对应于连续态的跃迁峰强度明显下降的现象, 这是由量子点基态与阱外连续态的波函数交叠随着偏压进一步增大而迅速减小导致的.     

Broadband light emitting from multilayer-stacked InAs/GaAs quantum dots

We report the effect of the GaAs spacer layer thickness on the photoluminescence(PL) spectral bandwidth of InAs/GaAs self-assembled quantum dots(QDs).A PL spectral bandwidth of 158 nm is achieved with a five-layer stack of InAs QDs which has a 11-nm thick GaAs spacer layer.We investigate the optical and the structural properties of the multilayer-stacked InAs/GaAs QDs with different GaAs spacer layer thicknesses.The results show that the spacer thickness is a key parameter affecting the multi-stacked InAs/GaAs QDs for wide-spectrum emission.     

Fabrication of quantum dot transistors incorporating a single self-assembled quantum dot

We report on the fabrication and the characterization of quantum dot transistors incorporating a single self-assembled quantum dot. The current–voltage characteristics exhibit clear staircase structures at room temperature. They are attributed to electron tunneling through the quantized energy levels of a single quantum dot.     

Pure spin-current diode based on interacting quantum dot tunneling junction

A magnetic field-controlled spin-current diode is theoretically proposed, which consists of a junction with an interacting quantum dot sandwiched between a pair of nonmagnetic electrodes. By applying a spin bias V_S across the junction, a pure spin current can be obtained in a certain gate voltage regime,regardless of whether the Coulomb repulsion energy exists. More interestingly, if we applied an external magnetic field on the quantum dot, we observed a clear asymmetry in the spectrum of spin current I_S as a function of spin bias, while the charge current always decays to zero in the Coulomb blockade regime. Such asymmetry in the current profile suggests a spin diode-like behavior with respect to the spin bias, while the net charge through the device is almost zero. Different from the traditional charge current diode, this design can change the polarity direction and rectifying ability by adjusting the external magnetic field, which is very convenient. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing.     

预先合成量子点组装制备高效量子点太阳电池

量子点太阳电池现已成为极具潜力的“第三代” 光伏器件, 其优点体现在材料成本低廉, 制备工艺简便, 以及其敏化剂特有的多激子效应(MEG) 潜能和吸光范围可方便调节等方面. 但是与染料分子敏化剂相比, 量子点敏化剂粒径更大、表面缺乏具有与TiO₂结合的官能团, 这导致其在TiO₂介孔中渗透阻力大、难以在TiO₂表面吸附沉积, 所以量子点沉积手段在电池组装过程中尤为重要. 本文综述了电池组装过程中量子点的沉积方法, 分类阐述了直接生长量子点方法: 化学浴沉积(CBD)和连续离子层吸附生长(SILAR), 以及采用预先合成量子点的沉积方法: 连接分子辅助法(LA)、直接吸附法(DA)和电泳沉积(EPD)方法, 陈述了各沉积方法的发展过程及相应电池性能的改善, 对比了这些沉积方法的优缺点. 突出介绍了预先合成量子点的沉积方法, 特别是近年来不断优化而凸显优势的连接分子辅助法(LA). 总结了此方法快速、均匀沉积以及实现器件高性能的特点, 介绍了此方法沉积表面缺陷更少、结构更完善、材料更“绿色化”的量子点敏化剂的最新研究成果.     

Bound polaron in quantum dot quantum well structures

The problem of bound polarons in quantum dot quantum well (QDQW) structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical (LO) and surface optical (SO) modes are derived in the framework of the dielectric continuum approximation. The electron--phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numerical results reveal that there exist three branches of eigenfrequencies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.     

Resonant Raman scattering from CdTe/ZnTe self-assembled quantum dot structures

We report resonant Raman scattering results of CdTe/ZnTe self-assembled quantum dot (QD) structures. Photoluminescence spectra reveal that the band gap energies of the CdTe QDs decrease with the increase of CdTe thickness from 2.0 to 3.5 monolayers, which indicates that the size of the QDs increases. When the CdTe/ZnTe QD structures are excited by non-resonant excitation, a longitudinal optical (LO) phonon response from the ZnTe barrier material is observed at 206 cm⁻¹. In contrast, when the CdTe/ZnTe QD structures are resonantly excited near the band gap energy of the QDs, additional phonon modes emerge at 167 and 200 cm⁻¹, while the ZnTe LO phonon response completely disappears. The 167 cm⁻¹ mode corresponds to the LO phonon of the CdTe QDs. A spatially resolved Raman scattering from the cleaved edge of the QD sample reveals that the 200 cm⁻¹ mode is strongly localized at the interface between the CdTe QDs and ZnTe cap layer. This phonon mode is attributed to the interface optical (IO) phonon. The analytically calculated value of the IO phonon energy using a dielectric continuum approach, assuming a spherical dot boundary, agrees well with the experimental value.     

新型成像技术的实验系统研究

光学相干层析成像是一种新型成像技术。超辐射发光二极管和超短脉冲飞秒激光是能满足成像系统要求的理想光源。在开展光学相干层析相关技术研究的基础上 ,建立了国内第一台上述两种光源的成像实验研究装置 ,对系统的横向、纵向分辨率等基本性能进行了测定 ;并对多种实际样品进行了层析成像。     

量子点环的电子输运研究

利用非平衡格林函数方法，研究了量子点环的相干输运性质. 结果表明：与一维量子点阵列 相比，量子点环中的电子出现更多新的准束缚能级. 量子点间耦合的增强会使微分电导振荡 出现退相干现象. 关键词： 量子点 电导     

Improved blue quantum dot light-emitting diodes via chlorine passivated ZnO nanoparticle layer

In blue quantum dot light emitting diodes (QLEDs), electron injection is insufficient, which would degrade device efficiency and stability. Herein, we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively. Moreover, it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel. As a result, the maximum external quantum efficiency of blue QLED was increased from 2.55% to 4.60%, and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device. Our work indicates that election injection plays an important role in blue QLED efficiency and stability.     

The strain relaxation of InAs/GaAs self-organized quantum dot

This paper presents a detailed analysis of the dependence of degree of strain relaxation of the self-organized InAs/GaAs quantum dot on the geometrical parameters. Differently shaped quantum dots arranged with different transverse periods are simulated in this analysis. It investigates the total residual strain energy that stored in the quantum dot and the substrate for all kinds of quantum dots with the same volume, as well as the dependence on both the aspect ratio and transverse period. The calculated results show that when the transverse period is larger than two times the base of the quantum dots, the influence of transverse periods can be ignored. The larger aspect ratio will lead more efficient strain relaxation. The larger angle between the faces and the substrate will lead more efficient strain relaxation. The obtained results can help to understand the shape transition mechanism during the epitaxial growth from the viewpoint of energy, because the strain relaxation is the main driving force of the quantum dot's self-organization.     

CdSe/HgSe/CdSe量子点量子阱(QDQW)晶粒的光学性质和电子结构

以CdSe纳米晶体为核,用胶体化学的方法,通过化学替代反应,获得了不同阱层或不同垒层的CdSeHgSeCdSe量子点量子阱(QDQW)晶体.紫外可见光吸收谱研究表明,通过调节QDQW中间HgSe阱层的厚度从0.9nm至0,可以调节QDQW颗粒的带隙从1.8变化至2.1eV,实现QDQW纳米晶体的剪裁.光致荧光(PL)谱研究显示,QDQW形成后,CdSeHgSe纳米颗粒表面态得到钝化,显现出发光强度加强的带边荧光峰.利用有效质量近似模型,对QDQW晶粒内部电子的1s—1s态进行了估算,估算结果总体趋势与实验数据相符 关键词： 量子点量子阱晶体 能带剪裁 加强的带边荧光峰     

Control of unpolarized emission in closely stacked InAs quantum dot structure

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.     

闪锌矿GaN/AlGaN量子点中激子态及光学性质的研究

在有效质量近似的框架下,运用变分方法研究闪锌矿GaN/AlGaN量子点中的激子态及相关光学性质,探讨电子与空穴在量子点中的三维空间受限和有限势效应.数值计算结果显示,当量子点的尺寸增加时, 量子尺寸效应对电子和空穴的影响减弱,基态激子结合能和带间光跃迁能也都降低;而当该量子点中垒层AlGaN中 Al含量增加时,提高了量子点对电子和空穴的束缚作用, 同时基态激子结合能和带间光跃迁能都增加.数值的理论结果与相关实验测量结果一致.     

Electron–phonon interaction in CdS/ZnS quantum dot

Electron–phonon effects on the two first electronic states in both CdS and GaAs quantum dots are investigated. Both confined longitudinal optical (LO) and surface optical (SO) phonons are considered. We use the intermediate-type variational approach. We find that, shifts caused by phonon contribution on electronic energies are more significant for CdS quantum dot. We find, also, that, contrary to GaAs based quantum dots, we shouldn’t neglect the SO phonon contribution for CdS based ones, especially for small dots.