Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma, Italy.
ACS Nano. 2013 May 28;7(5):3868-75. doi: 10.1021/nn401338v. Epub 2013 May 3.
Here we show a new effect due to the arsenic flux in the molecular beam epitaxy growth of InAs quantum dots on GaAs(001) at temperatures higher than 500 °C and high As/In flux ratio. We show that, by changing and tuning the direction of the As flux on a rippled substrate, a selective growth can be obtained where the dots form only on some appropriately orientated slopes of a sequence of mounds elongated along the [110] surface direction. Since the relative As flux intensity difference over the two opposite mound slopes is very small (2-5%), the observed large effect cannot be explained simply as a pure shadowing effect and reveals instead that As, whose contribution to the modeling of growth has often been ignored or underestimated, probably for a lack of knowledge, plays a fundamental role at these growth conditions. To explain our experiment, we have developed a kinetic model that explicitly takes into account the coupling between cations (In) and anions (As) and found that the very small surface gradient in the anion flux, due to the oblique evaporation on the mounded surface, is responsible for a massive drain of cations toward the surface anion-rich areas, thus generating the selective growth of quantum dots. We expect a comparable behavior for the anions of other III-V and II-VI compound semiconductors.
在这里，我们展示了在高于 500°C 的温度和高砷/铟通量比下，砷通量在分子束外延生长 InAs 量子点于 GaAs(001)上的新效应。我们表明，通过改变和调整波纹衬底上的砷通量方向，可以实现选择性生长，其中只有在沿着[110]表面方向伸长的一系列丘陵的某些适当取向的斜坡上形成点。由于两个相反的丘陵斜坡上的相对砷通量强度差异非常小（2-5％），因此不能简单地将观察到的大效应解释为纯阴影效应，而是表明砷在建模生长中经常被忽略或低估，可能是因为缺乏知识，在这些生长条件下起着至关重要的作用。为了解释我们的实验，我们开发了一个动力学模型，该模型明确考虑了阳离子（In）和阴离子（As）之间的耦合，并发现由于在丘陵表面上的斜蒸发，阴离子通量的表面梯度非常小，这导致阳离子大量流向表面富阴离子区域，从而产生量子点的选择性生长。我们预计其他 III-V 和 II-VI 化合物半导体的阴离子也会有类似的行为。
