Brehm Moritz, Grydlik Martyna, Tayagaki Takeshi, Langer Gregor, Schäffler Friedrich, Schmidt Oliver G
Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany. Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria.
Nanotechnology. 2015 Jun 5;26(22):225202. doi: 10.1088/0957-4484/26/22/225202. Epub 2015 May 13.
We investigate the optical properties of ordered Ge quantum dots (QDs) by means of micro-photoluminescence spectroscopy (PL). These were grown on pit-patterned Si(001) substrates with a wide range of pit-periods and thus inter QD-distances (425-3400 nm). By exploiting almost arbitrary inter-QD distances achievable in this way we are able to choose the number of QDs that contribute to the PL emission in a range between 70 and less than three QDs. This well-defined system allows us to clarify, by PL-investigation, several points which are important for the understanding of the formation and optical properties of ordered QDs. We directly trace and quantify the amount of Ge transferred from the surrounding wetting layer (WL) to the QDs in the pits. Moreover, by exploiting different pit-shapes, we reveal the role of strain-induced activation energy barriers that have to be overcome for charge carriers generated outside the dots. These need to diffuse between the energy minimum of the WL in and between the pits, and the one in the QDs. In addition, we demonstrate that the WL in the pits is already severely intermixed with Si before upright QDs nucleate, which further enhances intermixing of ordered QDs as compared to QDs grown on planar substrates. Furthermore, we quantitatively determine the amount of Ge transferred by surface diffusion through the border region between planar and patterned substrate. This is important for the growth of ordered islands on patterned fields of finite size. We highlight that the Ge WL-facets in the pits act as PL emission centres, similar to upright QDs.
我们通过微光致发光光谱（PL）研究有序锗量子点（QD）的光学性质。这些量子点生长在具有广泛坑周期以及因此具有不同量子点间距离（425 - 3400 nm）的坑图案化Si(001)衬底上。通过利用以此方式可实现的几乎任意的量子点间距离，我们能够选择对PL发射有贡献的量子点数量，其范围在70个到少于三个量子点之间。这个定义明确的系统使我们能够通过PL研究阐明几个对于理解有序量子点的形成和光学性质很重要的要点。我们直接追踪并量化从周围的润湿层（WL）转移到坑中的量子点的锗的量。此外，通过利用不同的坑形状，我们揭示了应变诱导的激活能垒的作用，对于在量子点外部产生的电荷载流子而言，必须克服这些能垒。这些电荷载流子需要在坑内和坑之间的润湿层的能量最小值与量子点内的能量最小值之间扩散。另外，我们证明在直立量子点成核之前，坑中的润湿层已经与硅严重混合，与在平面衬底上生长的量子点相比，这进一步增强了有序量子点的混合。此外，我们定量确定通过表面扩散穿过平面和图案化衬底之间的边界区域转移的锗的量。这对于在有限尺寸的图案化区域上生长有序岛很重要。我们强调坑中的锗润湿层小面充当PL发射中心，类似于直立量子点。
