Quantum dot (QD) is slated to play a significant role in quantum technologies through its usage as a single-photon source. It also has promising applications as efficient light emitters through strain-relaxed structures. This work demonstrates the fabrication of high-quality site controlled InGaN/GaN QDs through a large contribution of chemical etching in an otherwise reactive ion etching process. Uniform sized QDs with a hexagonal base and radii of 15 and 6 nm are fabricated and characterized by photoluminescence and femtosecond transient absorption spectroscopy. The natural exposition of the inherent hexagonal base is a signature of the reduced defects in these dots. The QDs show the intuitive additional quantum confinement due to size reduction, and the photoluminescence peaks manifest a blue shift. The absorption spectra indicate that the QDs are heavily strain-relaxed at smaller radii, and their characteristics as a function of size and pump power are investigated. The degree of strain relaxation and change in energy-band diagram as a function of position along the radius are also determined. The changes are prominent near the periphery, which creates a natural potential well for both electrons and holes, restricting the carriers from reaching the sidewalls. Femtosecond carrier dynamics indicate a lower capture rate for the smaller size of the dots, indicating excessive electrical or optical pumping will not necessarily lead to increased luminescence. The radiative decay of carriers is faster for strain-relaxed QDs due to higher oscillator strength originating from increased electron–hole wave function overlap. Higher pump power is found to decrease the radiative rate due to the increased effective size of the QDs and thereby reducing carrier injection density. This is in stark contrast to the frequently observed increased decay rate due to Auger recombination. Dynamic modification of the size of the QDs by pump power may find potential use in optoelectronic applications.

中文翻译：

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位置控制的六方InGaN / GaN隔离量子点中的飞秒第二载流子和光子动力学：天然径向势阱及其动态调制

量子点（QD）通过用作单光子源，有望在量子技术中发挥重要作用。作为通过应变松弛结构的高效发光器，它也具有广阔的应用前景。这项工作证明了在其他反应性离子蚀刻工艺中，化学蚀刻的巨大贡献可制造出高质量的InGaN / GaN QD。制作了六角形，半径分别为15和6 nm的均匀大小的QD，并通过光致发光和飞秒瞬态吸收光谱进行了表征。固有六角形基体的自然暴露是这些点中缺陷减少的标志。量子点由于尺寸减小而显示出直观的附加量子限制，并且光致发光峰表现出蓝移。吸收光谱表明，量子点在较小的半径处具有很大的应变松弛，并且研究了它们的特性与尺寸和泵浦功率的关系。还确定了应变弛豫的程度以及能带图中的变化与沿半径的位置的关系。这种变化在外围附近很明显，这为电子和空穴创造了自然势阱，从而限制了载流子到达侧壁。飞秒载流子动力学表明，对于较小尺寸的点，捕获率较低，这表明过多的电泵浦或光泵浦不一定会导致发光度增加。对于应变松弛的量子点，载流子的辐射衰减更快，这是由于电子-空穴波函数重叠增加而产生的更高的振荡器强度。发现更高的泵浦功率会由于QD的有效尺寸增加而降低辐射速率，从而降低载流子注入密度。这与由于俄歇重组而经常观察到的增加的衰减速率形成鲜明的对比。通过泵浦功率动态改变量子点的尺寸可能会在光电应用中找到潜在的用途。