The influence of digital alloy capping technique on the strain-coupled bilayer InAs quantum dots (QDs) has been presented. Multiple capping layers of different composition have been utilized instead of a single thick capping layer to reduce the overall strain inside the heterostructure. In bilayer QDs, the propagation of residual strain from the lower QD layer to the top QD layer introduces defects and dislocations. By using the digital alloy technique over the conventional or analog alloy capping technique, the surface defects could be minimized and the crystallinity could be improved. In this study, four different capping materials have been considered, viz. two ternary materials (InxGa1-xAs and GaAs1-xSbx) and two quaternary materials (InxAlyGa1-x-yAs and InxGa1-xAs1-ySby) for analysis of both analog alloy and digital alloy techniques. The strain and energy band profile has been computed for all the heterostructures using Nextnano software. The biaxial and hydrostatic strain have been computed and compared to understand the strain distribution within the heterostructures. The ground state emission wavelength was found red shifted for the InAs bilayer QD heterostructure with digital alloy capping layers as compared to that of the analog alloy capping. Moreover, the choice of capping materials exhibits both type-I and type-II energy band alignment which is suitable for different optoelectronic applications. This comparative study of analog and digital alloy capping layer for the bilayer QDs would definitely help in optimization of the device heterostructures with minimal strain and defects.

中文翻译：

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数字合金覆盖层对双层自组装 InAs 量子点异质结构的影响

已经介绍了数字合金封盖技术对应变耦合双层 InAs 量子点 (QD) 的影响。已使用不同成分的多个覆盖层而不是单个厚覆盖层来降低异质结构内部的整体应变。在双层 QD 中，残余应变从较低的 QD 层传播到顶部的 QD 层会引入缺陷和位错。通过使用数字合金技术而不是传统或模拟合金封盖技术，可以最大限度地减少表面缺陷并提高结晶度。在这项研究中，已经考虑了四种不同的封盖材料，即。两种三元材料（InxGa1-xAs 和 GaAs1-xSbx）和两种四元材料（InxAlyGa1-x-yAs 和 InxGa1-xAs1-ySby），用于分析模拟合金和数字合金技术。使用 Nextnano 软件计算了所有异质结构的应变和能带分布。已经计算并比较了双轴和流体静力应变，以了解异质结构内的应变分布。与模拟合金覆盖层相比，具有数字合金覆盖层的 InAs 双层 QD 异质结构的基态发射波长被发现红移。此外，封端材料的选择表现出 I 型和 II 型能带排列，适用于不同的光电应用。这种对双层 QD 的模拟和数字合金覆盖层的比较研究肯定有助于优化具有最小应变和缺陷的器件异质结构。