We investigated metal-organic vapor phase epitaxy grown (InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots (QDs) with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography (APT). The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution, which provides detailed structural and compositional information on the system. The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our sample with a very high density of ∼4 × 10¹¹ cm⁻². APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb. Finite element (FE) simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface. The composition of the QDs is estimated by combining the results from X-STM and the FE simulations, yielding ∼In_xGa_1 − xAs_1 − ySb_y, where x = 0.25–0.30 and y = 0.10–0.15. Noticeably, the reported composition is in good agreement with the experimental results obtained by APT, previous optical, electrical, and theoretical analysis carried out on this material system. This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed. A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer, where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation. Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.

我们通过横截面扫描隧道显微镜 (X-STM) 和原子探针研究了金属有机气相外延生长 (InGa)(AsSb)/GaAs/GaP Stranski-Krastanov 量子点 (QD) 在 QD-Flash 存储器中的潜在应用断层扫描（APT）。X-STM 和 APT 的组合是研究具有原子分辨率的半导体异质结构的非常强大的方法，它提供了有关系统的详细结构和组成信息。发现相当小的 QD 是具有非常小的顶面的截棱锥形状，并且出现在我们的样品中，密度非常高，约为4 × 10 ¹¹  cm ^-2. APT 实验表明 QD 富含 GaAs，含有少量 In 和 Sb。使用来自 X-STM 的结构数据进行有限元 (FE) 模拟，以计算解理表面的晶格常数和向外松弛。通过结合 X-STM 和有限元模拟的结果，估计 QD 的组成，产生∼ In _x Ga _{1 −  x} As _{1 −  y} Sb _y，其中x  = 0.25–0.30 和y = 0.10–0.15。值得注意的是，报告的成分与 APT 获得的实验结果非常吻合，之前对该材料系统进行了光学、电学和理论分析。这证实了参与 QD 形成的 InGaSb 和 GaAs 层已经强烈混合。QD 覆盖层的详细分析显示 Sb 和 In 从 QD 层分离，其中 APT 和 X-STM 均表明 Sb 主要位于 QD 之外，证明 Sb 在点形成过程中主要充当表面活性剂。我们的结构和成分分析提供了对这种新型 QD 系统的宝贵见解，并为进一步优化增长以提高 QD-Flash 存储设备的存储时间提供了途径。