Development of Polarization-Independent Absorption Edge of Shape-Controlled Quantum Dots

高质量自组装量子点的最新进展有助于量子点半导体光放大器（soa）等新型光学器件的发展。在实际应用中，极化特性的控制是开发与极化无关的soa的先决条件。为了实现偏振不敏感带，我们提出了一种使用形状控制量子点的新方法。在紧密堆叠的Stranski-Krastanov （S-K）模式InAs量子点，即柱状量子点中，通过堆叠S-K模式生长层，成功地人工控制了高度，从而改变了量子约束方向。采用分子束外延法生长出具有柱状量子点的SOA结构。观察到每一层上的岛屿在垂直方向上相互接触，因此堆叠的岛屿结构整体上呈柱状。柱状量子点直径约为17 nm。高度由堆叠层数（SLN）控制。SLN为8的典型高度约为13 nm。线性光致发光（PL）偏振光谱测量从一个切割，未涂层的边缘表面的样品。沿面内（生长）方向设置分析仪测量TE （TM）模式PL。在紧密堆叠的InAs/GaAs自组装量子点中，半导体光放大器的偏振不灵敏度被精确控制。所获得的偏振不敏感带宽大于40nm。这些结果表明，通过控制量子点形状可以实现宽带极化不敏感。

Recent advance in high-quality self-assembled QDs contributes to the development of new optical devices such as QD semiconductor optical amplifiers (SOAs). For practical applications, control of the polarization property is prerequisite for developing polarization-independent SOAs. To accomplish the polarization insensitive bandedge, we propose a new approach using shape-controlled QDs. In closely stacked Stranski-Krastanov (S-K)-mode InAs QDs, namely, columnar QDs, the height has been successfully controlled, artificially, by stacking the S-K-mode growth layer, which can change the quantum-confinement direction. SOA structures with columnar QDs were grown by molecular beam epitaxy. The islands on each layer were observed to be in contact with each other in the perpendicular direction, so that the stacked island structure, as a whole, becomes columnar in shape. The diameter of the columnar QDs is about 17 nm. The height was controlled by the stacking layer number (SLN). The typical height for the SLN of 8 is about 13 nm. Linear-photoluminescence (PL) polarization spectra were measured from a cleaved, uncoated edge surface of the sample. The TE (TM)-mode PL was measured by setting an analyzer along the in-plane (growth) direction. Polarization insensitivity of semiconductor optical amplifier has been shown to be precisely controlled in closely stacked InAs/GaAs self-assembled quantum dots. The polarization insensitive bandwidth achieved is larger than 40nm. These results demonstrate that wideband polarization insensitivity has been accomplished by controlling QD shape.