Figure 6
TEM micrographs of Ge DQDs formed at the sidewall corners of 30 nm-wide poly-Si ridges by thermal oxidation at 900 °C for (a) 10.5 min, (b) 27 min, and (c) 40 min. The depth of penetration of Ge QDs within the Si3N4 spacer layers is enhanced by increasing thermal oxidation time, leading to the reduction in the inter-dot spacing between the DQDs. The reduction in the inter-dot spacing with increasing thermal oxidation time is also evidenced for Ge DQDs in the cases of 60 nm-wide poly-Si nanoridges as shown for (d) 10.5 min and (e)27 min oxidation time. A longer oxidation process not only increases the penetration of Ge QDs through the Si3N4 layers, making the pair of QDs closer to each other, but also improves the crystallinity of the Ge QDs as shown in the HRTEM observations for (f) 10.5 min and (g) 27 min thermal oxidation at 900 °C.
