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。     

科学家成功将单光子源用于量子通讯技术

量子通讯遇到的一个最大问题是如何得到单光子，它们能保证量子体系的安全和高效性。一旦拥有充足的单光子源，量子系统就能以接近光速的速度传递信息。     

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。     

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.     

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。     

科学家实现世界最佳单光子源

由潘建伟院士和陆朝阳教授等组成的科研团队在国际上首次实现了基于量子点脉冲共振荧光的确定性高品质单光子源。该研究工作最近以长文的形式发表在《自然》杂志的子刊《自然·纳米技术》上。这是我国在量子点光学量子操纵领域发表在《自然》系列期刊上第一篇论文。审稿人称赞这是一个“令人惊喜的高质量实验”。     

尺寸分布和界面混合对InAs/GaAs量子点光学性质的影响

研究了自组织生长模式(S-K modes)下量子点尺寸的不均匀分布对量子点发光性质的影响,对其光致发光峰进行了拟合计算.研究发现,量子点尺寸的不均匀分布导致了量子点发光峰的展宽以及发光峰位的红移.另一方面,后处理工艺中的退火及质子注入引起的界面混合导致了量子点PL谱发光峰的蓝移及半高宽的减小.     

1.5微米波段GaAs基异变InAs量子点分子束外延生长

1.55微米波段GaAs基近红外长波长材料在光纤通讯,高频电路和光电集成等领域有潜在的应用价值。本文用分子束外延方法研究了GaAs基异变InAs量子点材料的生长,力图实现在拓展量子点发光波长的同时保持或增加InAs量子点的密度。在实验中,首先优化了In0.15GaAs异变缓冲层的生长,研究了生长温度和退火对减少穿通位错的作用。在此基础上,优化了长波长InAs量子点的生长。最终在GaAs基上获得了温室发光波长在1491nm,半高宽为27.73meV,密度达到4×1010cm-2的InAs量子点。     

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。     

InAs/GaAs自组织量子点的可控分子束外延生长及其新型光电器件研究北大核心CSCD

半导体量子点因其具有类原子的分立能级结构,可在三维方向上对载流子运动进行束缚,因此被认为是光发射器件(激光器、量子光源等)极具前景的有源物质之一。其器件的性能强烈依赖于量子点材料的品质、光场与量子点偶极子场的有效相互作用等。本文将从半导体InAs/GaAs自组织量子点的可控分子束外延生长调控技术出发,进一步探讨应用于光通信、片上光互联领域的量子点激光器,以及应用于光量子信息领域的高品质量子光源器件。     

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.     

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.     

Fabrication of InAs quantum dots on silicon

Reflection high-energy electron diffraction and scanning tunneling microscopy have been used to demonstrate for the first time that InAs quantum dots may be fabricated directly on Si(100) by molecular beam epitaxy. It is shown that heteroepitaxial growth in an InAs/Si system takes place by the Stranski-Krastanow mechanism and the surface morphology depends strongly on the substrate temperature. Pis’ma Zh. Tekh. Fiz. 24, 10–15 (April 26, 1998)     

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.     

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.     

Photoluminescence and magnetophotoluminescence of circular and elliptical InAs/GaAs quantum dots

Photoluminescence, magnetophotoluminescence, and atomic force microscopy were used for the characterization of MOVPE prepared InAs/GaAs quantum dots. Significant differences in the behaviour of the first excited photoluminescence transition in magnetic field are explained by the different lateral shape of quantum dots. While the first excited luminescence peak of circular quantum dots splits with increasing magnetic field into two peaks, no splitting occurs for quantum dots with elliptic shape, only small red shift is observed. Theoretical calculations of energy levels in InAs/GaAs quantum dots with circular and elliptical shape with different elongations are presented and compared with experimental results.     

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.     

Structural characterization of GaSb-capped InAs/GaAs quantum dots with a GaAs intermediate layer

GaSb incorporation to InAs/GaAs quantum dots is considered for improving the opto-electronic properties of the systems. In order to optimize these properties, the introduction of an intermediate GaAs layer is considered a good approach. In this work, we study the effect of the introduction of a GaAs intermediate layer between InAs quantum dots and a GaSb capping layer on structural and crystalline quality of these heterostructures. As the thickness of the GaAs intermediate layer increases, a reduction of defect density has been observed as well as changes of quantum dots sizes. This approach suggests a promising method to improve the incorporation of Sb to InAs heterostructures.