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.     

温度对InAs/GaAs量子点生长影响的动力学蒙特卡罗模拟

采用动力学蒙特卡罗模型模拟了GaAs应变弛豫图形衬底上InAs量子点阵列生长早期阶段,温度对浸润层之上第一层亚单原子层阶段的影响.通过对生长表面形态、岛平均大小、岛大小分布及其标准差等方面的研究,证明了通过控制温度能够得到大小均匀、排列有序的岛阵列,这对后续量子点生长的定位和尺寸控制有重要影响.     

Ge基GaAs薄膜和InAs量子点MBE生长研究

采用分子束外延(MBE)法,在优化Ge衬底退火工艺的基础上,通过对比在(001)面偏<111>方向分别为0°、2°、4°和6°的Ge衬底上生长的GaAs薄膜,发现当Ge衬底的偏角为6°时有利于高质量GaAs薄膜的生长;通过改变迁移增强外延(MEE)的生长温度,发现在GaAs成核温度为375℃时,可在6°偏角的Ge衬底上获得质量最好的GaAs薄膜。通过摸索GaAs/Ge衬底上InAs量子点的生长工艺,实现了高效的InAs量子点光致发光,其性能接近GaAs衬底上直接生长的InAs量子点的水平。     

InP(001)基衬底上自组织生长InAs量子点(线)的光学性质研究

在InP(001)基衬底上用分子柬外延方法生长InAs纳米结构材料，通过衬底的旋转与否及混合生长模式，得到了两种InAs量子点和量子线，并研究了量子点、线的光学性质，结果表明，两种方式都可生长出较强发光的量子点(线)；由量子点排列构成的量子线的光致发光光谱呈现出多峰结构，分析和理论计算表明这是InAs量子线上各量子点在垂直方向上不同高度分布和非连续性而造成的。     

自组织InAs/GaAs量子点的X射线双晶衍射研究

用X射线双晶衍射方法测定了自组织生长的InAs／GaAs量子点的摇摆曲线，根据Takagi-Taupin方程对曲线进行了拟合。在考虑量子点层晶格失配的情况下，理论曲线和实验曲线符合得很好，从而确定了量子点垂直样品表面的失配度，约为4～6％，这与宏观连续体弹性理论的预测相近。结合电镜、原子力显微镜的观察结果表明对子单层沉积方法获得的量子点层采用化合物构层进行拟合所得结果是合理的。     

延长自组织InAs／GaAs量子点发光波长的研究进展

在近几年的InAs／GaAs自组织量子点的研究中，如何荻得1．3～1．55μm。长波长量子点材料是一个很热门的课题。本文综述了各种延长自组织InAs／GaAs量子点发光波长的方法，并提出了实用化的最佳途径。     

单光子源低密度长波长InAs／GaAs量子点的制备

通过优化分子束外延生长条件,得到室温发光在1300nm低密度的自组织InAs/GaAs量子点.使用极低的InAs生长速率(0.001单层/秒)可以把量子点的密度降低到4×106cm-2.这些结果使得InAs/GaAs量子点可以作为单光子源应用在未来的光纤基量子密码、量子通信中.     

应力补偿技术在InAs/GaAs量子点中的研究现状

通过在多层量子点体系中引入应变补偿层,改变量子点系统的应力场分布,可以控制生长过程中量子点的大小均匀性和密度,最终获得高质量、高密度的多层量子点体系,应用到量子点光电器件中,可改善器件的电学和光学性能。介绍了应变补偿层在量子点体系中作用的原理,常用的应变补偿材料体系,以及目前国内外对应变补偿技术的研究状况,最后提出了现存的问题和今后的发展方向。     

碳量子点的氨基化及其对发光性能的影响

利用水热反应釜的条件,使碳量子点的含氧基团与氨水反应,实现了碳量子点的表面氨基化。制备的氨基化碳量子点尺寸分布均匀,总的含氮量受反应温度影响。实验结果表明:氨基化后的碳量子点荧光发射性质明显优于未氨基化的碳量子点;氨基化的氮源及其氮源加入反应过程中的顺序均会影响碳量子点的荧光发射效率。通过实验设计,确定出了氨基化碳量子点的最佳制备条件,从而为碳量子点的光学性质调控及应用奠定了技术支持。     

1.08μmInAs/GaAs量子点激光器光学特性研究

介绍了ＩｎＡｓ／ＧａＡｓ量子点激光器的材料生长,器件制备及其光学特性的研究。器件为条宽１００μｍ,腔长１６００μｍ未镀膜激器。室温阈值电流密度为２２１Ａ／ｃｍ＾２,激射波长为１．０８μｍ,连续波工作最大光功率输出为２．７４Ｗ（双面）,外微分效率为８８％,经５０℃,１０００ｈ老化,仍有〉１．２Ｗ的光功率输出。     

Effect of size non-uniformity on photoluminescence from ensembles of InAs quantum dots embedded in GaAs

The photoluminescence (PL) spectrum from ensembles of InAs/GaAs quantum dots (QDs) is calculated. The effect of the dot size distribution and the variation of the associated confining potentials on the PL spectra are estimated. It is found that the intermixing of the interfaces causes an increase of the PL spectra energy. The size distribution determines the spectrum width and makes the PL line shape asymmetric with a high-energy tail. Moreover, the non-uniform size distribution also results in a redshift of the PL peak. The experimental PL spectrum is well explained by the size distribution and intermixing effect within the effective mass approximation.     

Inhomogeneous broadening and alloy intermixing in low proton dose implanted InAs/GaAs self-assembled quantum dots

In this work, low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) experiments have been carried out to investigate the optical and electronic properties of InAs/GaAs quantum dots (QDs) subjected to room-temperature proton implantation at various doses (5 × 10(10)-10(14)?ions?cm(-2)) and subsequent thermal annealing. The energy shift of the main QD emission band is found to increase with increasing implantation dose. Our measurements show clear evidence of an inhomogeneous In/Ga intermixing at low proton implantation doses (≤5 × 10(11)?ions?cm(-2)), giving rise to the coexistence of intermixed and non-intermixed QDs. For higher implantation doses, a decrease of both the PL linewidth and the intersublevel spacing energy have been found to occur, suggesting that the dot-size, dot-composition and dot-strain distributions evolve towards more uniform ones.     

Thermal-induced intermixing effects on the optical properties of long wavelength low density InAs/GaAs quantum dots

The effect of post-growth rapid thermal annealing on the photoluminescence properties of long wavelength low density InAs/GaAs (001) quantum dots (QDs) with well defined electronic shells has been investigated. For an annealing temperature of 650 °C for 30 s, the emission wavelength and the intersublevel spacing energies remain unchanged while the integrated PL intensity increases. For higher annealing temperature, blue shift of the emission energy together with a decrease in the intersublevel spacing energies are shown to occur due to the thermal activated In–Ga interdiffusion. While, this behaviour is commonly explained as a consequence of the enrichment in Ga of the QDs, the appearance of an additional exited state for annealing temperatures higher than 650 °C suggests a variation of the intermixed QDs's volume/diameter ratio toward QDs's enlargement.     

Room-temperature photoluminescence at 1.55 μm from heterostructures with InAs/InGaAsN quantum dots on GaAs substrates

Room-temperature photoluminescence (PL) at 1.55 μm from heterostructures with InAs/InGaAsN quantum dots (QDs) grown by MBE on GaAs substrates is demonstrated for the first time. The effect of nitrogen incorporated into InAs/InGaAsN QDs on the PL wavelength and intensity was studied. The integral intensity of PL from the new structure with InAs/(In)GaAsN QDs is comparable to that from a structure with InGaAsN quantum wells emitting at 1.3 μm.     

Statistics of electron emission from InAs/GaAs quantum dots

A theoretical treatment for thermal and tunneling emission of electrons from InAs/GaAs quantum dots is performed to achieve “effective emission rates” corresponding to experimentally obtained quantities. From these results, Arrhenius graphs are calculated using parameter values for quantum dots with 20/10 nm base/height dimension. Emission from the electron s shell as direct transitions, as two-step transitions from the s to the p shell, as thermal transitions from s to p followed by tunneling and as direct tunneling from the s and the p shell to the GaAs conduction band is taken into account. Due to the varying emission possibilities, Arrhenius graphs appear with complicated shapes depending on quantities originating from structural and electronic properties of the quantum dots.     

Morphology and composition of InAs/GaAs quantum dots

Surface compositional maps of self-organized InAs/GaAs quantum dots were obtained with laterally resolved photoemission spectroscopy. We found a surface In concentration of about 0.85 at the center of the islands which decreases to 0.75 on the wetting layer. Comparison with concentration values found in the core of similar dots suggests a strong In segregation on the topmost surface layers of the dots and on the surrounding wetting layer. Furthermore, the morphological properties of the dots such as size and density have been measured with plan-view transmission electron microscopy and low energy electron microscopy.     

Deep levels induced by InAs/GaAs quantum dots

Self-organised InAs/GaAs quantum dots (QDs) were formed by molecular beam epitaxy using the Stranski–Krastanov growth mode. Deep-level transient spectroscopy as well as secondary ion mass spectrometry have been used to characterise structures containing the QDs. DLTS depth profiling procedures indicate that deep level-related defects are localised in GaAs in the vicinity of the QD plane. For the first time, we report the presence of a deep level-related trap with an extremely high thermal activation energy of E_c − 1.03 eV. An electron trap at E_c − 0.78 eV can be identified as the well-known level related to the EL2 family. We conclude that a third trap revealed at E_c −0.57 eV is the familiar PL killer related to the intrinsic point defect-oxygen complex. The latter is confirmed by results of the SIMS study, which indicates that the amount of oxygen accumulated at the InAs/GaAs heterointerface is increased. This paper demonstrates that the EL2 and oxygen-related deep-level centers occur by the presence of InAs/GaAs QDs. We present the hypothesis that deep states could be a factor limiting the efficiency of QD-based devices.     

Effect of temperature on the growth of InAs/GaAs quantum dots grown on a strained GaAs layer

We have studied the effect of temperature on the growth of InAs quantum dots (QDs) grown on a strained GaAs layer. The 2.0 nm thick, strained GaAs was obtained by growing it on a relaxed In0.15Ga0.85As layer. We observed that the density of QDs grown in this manner strongly depends on the growth temperature. A change in the growth temperature from 510 degrees C to 460 degrees C resulted in a large increase in the QD density from 2.3 x 10(10) cm(-2) to 6.7 x 10(10) cm(-2) and a sharp reduction in their height from 8.0 nm to 3.0 nm. Photoluminescence (PL) results from these QDs are also presented.     

Defects in nanostructures with ripened InAs/GaAs quantum dots

InAs/GaAs quantum dot (QD) structures were grown by molecular beam epitaxy (MBE) with InAs coverages θ continuously graded from 1.5 ML to 2.9 ML. A critical coverage of 2.23 ML is found, above which the islands undergo ripening, which causes a fraction of quantum dots to increase in size and to eventually relax through the formation of pure, edge-type misfit dislocations which propagate towards the surface in the form of V-shaped defects. Concomitant with ripening, extended-defect related traps with activation energies of 0.52 and 0.84 eV were observed, and regarded as the cause of the significant worsening of the optical and electrical properties in high coverage structures. Their relationship with the observed dislocations is discussed.