NER: Engineering of InAs Quantum Dot Ensembles Using Interference of Optical Surface Waves

利用光学表面波干涉的InAs量子点集成工程本项目解决了通过应力驱动的Volmer-Weber或Stranski-Krastanov生长机制形成的量子点（QD）外延半导体集成尺寸分布不均匀加宽的问题。量子点的均匀性和窄的尺寸分布是量子点结构在光电子器件中应用的主要挑战。本研究的主要目的是利用光学表面波的干涉效应来评估GaAs表面InAs量子点成核过程的纳米级控制的可行性。在分子束外延（MBE）生长量子点的过程中，利用脉冲紫外激光在衬底表面产生干涉图样。该图案的典型周期为数百nm，将使用两种不同的光学方案来创建：（i）入射波与散射相干表面波的干涉;以及（ii）入射波与耦合到分裂激光束的两个表面波的干涉。光干涉图样在100-200 nm范围内周期性地调制衬底的表面性质。量子点的成核可以通过调节衬底温度来控制，从而破坏驻波图的波腹处的成核团簇，或者通过激光烧蚀来控制表面的起伏来控制表面能。100 nm的调制尺度有望形成初始量子点成核的模板，随后量子点系综的演化将驱动向更高密度的量子点，（3-10）e10 cm-2。原位光学冲击的重要特点是它不会在表面留下任何残留物，可以在生长过程中进行，并且可以调节以引入最小的缺陷密度，我们将系统地研究影响因素（生长温度，As流量，生长速率，激光功率等）。其提供均匀且窄QD分布和有效发光。利用光控成核生长的样品将通过原位RHEED以及STM、TEM和光致发光方法进行研究，以揭示生长参数与量子点系统的结构和性质之间的相关性。该研究所的实验室拥有量子点表征所需的所有设备。这包括最先进的场发射超高分辨率TEM、聚焦离子束工作站、表面分析工具、五种STM工具（可配置用于不同成像模式和超高真空环境）以及独特的超声力显微镜。拟议工作的成功完成将对各种光电元件的性能产生重大影响。该方法将允许生长具有尖锐尺寸分布和高辐射复合效率的量子点结构。例如，量子点结构将被用作激光二极管的活性介质，具有上级性能特征，例如更高的效率、更高的热稳定性、更高的调制频率和增加的可靠性。

Engineering of InAs Quantum Dot Ensembles Using Interference of OpticalSurface WavesThis project addresses the problem of inhomogeneous broadening of the sizedistribution of quantum dot (QD) epitaxial semiconductor ensembles formedvia a stress-driven Volmer-Weber or Stranski-Krastanov growth mechanism. Theuniformity and narrow size distribution of the QDs are the major challengesfor the utilization of QD structures in optoelectronic devices. The primarygoal of this proposal is to evaluate the feasibility of nanoscale control ofthe nucleation process of InAs QDs on a GaAs surface using the interferenceof the optical surface waves. The interference pattern will be generated onthe surface of the substrate using a pulsed UV laser during the growth ofQDs by molecular beam epitaxy (MBE). The pattern, with a typical period offew hundred nm, will be created using two different optical schemes basedon: (i) the interference of the incident wave with the scattered coherentsurface wave; and (ii) the interference of the incident waves with twosurface waves coupled to the split laser beams. The optical interferencepattern will modulate periodically the surface properties of the substrateat 100-200 nm level. The nucleation of QDs will be controlled through eithersubstrate temperature modulation, thereby destroying the nucleation clustersin the antinode of the standing wave pattern, or through undulation of thesurface by laser ablation to control the surface energy. The 100-nmmodulation scale is expected to form a template for initial QD nucleation,and the subsequent evolution of the QD ensemble will be driventhermodynamically towards higher density of dots, (3-10)e10 cm-2. Theimportant features of the in-situ optical impact are that it does not leaveany residues on the surface, can be conducted during the growth process, andcan be adjusted to introduce the minimum defect density.We will systematically investigate the factors (growth temperature, As flux,growth rate, laser power, etc.) that provide uniform and narrow QDdistribution and efficient luminescence. The samples grown using opticallycontrolled nucleation will be studied by the in-situ RHEED, as well as STM,TEM and photoluminescence methods to reveal the correlations between growthparameters, and the structure and properties of the QD systems. Thelaboratories at the Institute have all the necessary equipment for the QDcharacterization. This includes state-of-the-art field-emission ultra-highresolution TEM, focused ion beam station, surface analysis tools, five STMtools configured for different imaging modes and environment includingultra-high vacuum, and unique ultrasonic force microscope.The successful completion of the proposed work would have a significantimpact on the performance of various optoelectronic components. The methodwill allow the growth of QD structures with sharp size distribution and highradiative recombination efficiency. For example, the QD structures will beused as active media for laser diodes with superior performancecharacteristics, such as higher efficiency, higher thermal stability, highermodulation frequency and increased reliability.