Improved nanocrystal formation,quantum confinement and carrier transport properties of doped Si quantum dot superlattices for third generation photovoltaics

An all‐Si tandem solar cell has the potential to achieve high conversion efficiency at low cost. However, the selection and synthesis of candidate material remain challenging. In this work, we show that the conventional ‘Si quantum dots (Si QDs) in SiO₂ matrix’ approach can lead to the formation of over‐sized Si nanocrystals especially when doped with phosphorous, making the size‐dependent quantum confinement less effective. Also, our investigation has shown that the high resistivity of this material has become the performance bottleneck of the solar cell. To resolve these matters, we propose a new design based on Si QDs embedded in a SiO₂/Si₃N₄ hybrid matrix. By replacing the SiO₂ tunnel barriers by the Si₃N₄ layers, the new material manages to constrain the growth of doped Si QDs effectively and enhances the apparent band gap, as shown in X‐ray diffraction, Raman, photoluminescence and optical spectroscopic measurements. Besides, electrical characterisation on Si QD/c‐Si heterointerface test structures indicates the new material possesses improved vertical carrier transport properties. Copyright © 2011 John Wiley & Sons, Ltd.     

冷原子束或超冷原子束的产生及其应用

综述了冷原子束或超冷原子束产生的基本原理、方法和实验结果及其最新进展.重点介绍了建立在激光冷却(多普勒、亚多普勒和亚反冲冷却机制)和磁光阱技术基础上的冷原子束或超冷原子束产生方案,并简单介绍了冷原子束或超冷原子束在基础物理问题研究和原子光学等领域中的应用.     

小垂直发散角大光腔980nm单模InGaAs/GaAs/AlGaAs量子阱激光器

通过采用经过优化的新型大光腔结构,脊形波导980nm单模InGaAs/GaAs/AlGaAs多量子阱半导体激光器在保持大功率光输出的同时获得了较小的垂直发散角.结果表明波导中的光功率密度可以降低,获得了大于400mW、斜率效率0.89W/A的输出光功率,垂直方向远场发散角也降低到23°.     

极化可区分光子的双光子干涉

双光子干涉本质是整体状态不可区分.两光子可区分而整体态不可区分时,仍然能发生双光子干涉.将HOM型与Franson型双光子干涉相结合,提出一个可实现两光子可区分而整体态不可区分的双光子干涉实验方案.此双光子干涉实验方案中两光子极化方向相互垂直,但方案中并不擦除两光子的极化可区分信息.     

Quantum secret sharing between multiparty and multiparty with entanglement swapping

A quantum secret sharing （QSS） protocol between multiparty and multiparty is proposed, based on Greenberger-Horne- Zeilinger （GHZ） state. The protocol utilizes quantum Fourier transform and entanglement swapping to achieve a high intrinsic efficiency and source capacity. Then, the security of this protocol against some possible eavesdropping strategies has been analyzed. Furthermore, the presented protocol is generalized to the d-level case.     

High power λ～8.5 μm quantum cascade laser grown by MOCVD operating continuous-wave up to 408 K

Robust quantum cascade laser(QCL)enduring high temperature continuous-wave(CW)operation is of critical import-ance for some applications.We report on the realization of lattice-matched InGaAs/lnAIAs/InP QCL materials grown by metal-organic chemical vapor deposition(MOCVD).High interface quality structures designed for light emission at 8.5μmare achieved by optimizing and precise controlling of growth conditions.A CW output power of 1.04 W at 288 K was obtained from a 4 mm-long and 10 μm-wide coated laser.Corresponding maximum wall-plug efficiency and threshold current density were 7.1％and 1.18 kA/cm2,respectively.The device can operate in CW mode up to 408 K with an output power of 160 mW.     

量子阱材料折射率低偏振相关性研究

分析了阱宽、垒高和应变对量子阱材料TE模和TM模折射率的影响,并剖析了其中的物理机理.研究表明:对于量子限制效应带来的量子阱折射率偏振相关性,阱宽越小或垒高越高,折射率偏振相关性越大.压应变增大时,折射率偏振相关性增大,张应变可以克服量子限制效应带来的折射率偏振影响.对于不同阱宽和垒高的量子阱,均存在合适的张应变量使折射率偏振相关性最小,且阱宽越小或垒高越高所需的张应变量越大.根据以上分析,提出量子阱材料折射率低偏振相关设计方法,并据此设计出C波段(1 530～1 565 nm)内折射率低偏振相关(小于0.03)的量子阱材料In0.49Ga0.51As/In0.77Ga0.23As0.5P0.5.研究结果有助于优化设计光网络中关键器件.     

基于太赫兹辐射的甘草主成分光谱分析

采用透射式太赫兹时域光谱系统测试了甘草主成分甘草酸、甘草次酸以及甘草苷的太赫兹光谱,发现甘草酸、甘草次酸以及甘草苷在0.3～1.72 THz频段内具有明显的吸收特征,此频段内它们的太赫兹吸收峰峰位接近、吸收谱谱线相似.利用量子化学方法模拟甘草酸的太赫兹吸收谱,并与实验谱进行对比指认完成对3种单质的定性分析工作.本文分别...     

不同自旋量子相干的密度矩阵计算

本文利用密度矩阵的对称共轭性,提出一个在弱相互作用下,方便地计算量子相干的方法。首先推导出纯体系的各种公式,然后计算不同自旋四种混合体系的各种量子相干。获得了它们的数目的比值以及它们的总和。推导出混合体系的各种公式。除理论计算外,还扼要地讨论这一研究结果的意义。     

量子密钥分发系统的现实无条件安全性

量子密钥分发系统由于能够提供一种物理上安全的密钥分发方式,因此成为量子信息领域的研究热点,其中如何在现实条件下保证量子密钥分发的无条件安全性是该领域的一个重要研究课题。本文从经典保密通信系统中具有完善保密性的一次一密体制出发,介绍了量子密钥分发系统的应用模型和整体保密通信系统的安全性基础,以及自量子密钥分发协议被提出以来量子密钥传输现实无条件安全性的研究进展,重点介绍了针对现实条件安全漏洞的各种类型的量子黑客攻击方案、防御方式,以及最近两年被广泛重视的与测量设备无关的量子密钥分发系统的理论和实验进展。