Humble planar defects in SiGe nanopillars

We report a {001} planar defect found in SiGe nanopillars. The defect structure, determined by atomic-resolution electron microscopy, matches the Humble defect model proposed for diamond. We also investigate several possible variants of the Humble structure using first-principles calculations and find that the one lowest in energy is in agreement with the scanning transmission electron microscope images. The pillar composition has been analyzed with electron energy loss spectroscopy, which hints at how the defect is formed. Our results show that the structure and formation process of defects in nanostructured group IV semiconductors can be different from their bulk counterparts.

Figure 1

Atomic structure of the SiGe Humble defect. (a) Low-magnification HAADF-STEM images of the SiGe pillar. Scale bar: 10 nm. The planar defect in this pillar is indicated by the two red arrows. (b) Atomic-resolution HAADF-STEM images of the defect viewed from [110] projection, and (c) from [210] projection, with the structural models shown superimposed. Scale bar: 3 Å.

Figure 2

Structural models of the five Humble defects proposed by Goss et al. viewed from the [001], [110], and [210] axes, defined relative to the bulk lattice. Atoms shown in red and purple indicate the upper and lower atoms that are under significant bond angle distortion.

Figure 3

Experimental defect structure compared with DFT-calculated ones. (a) HAADF intensity profiles of the HAADF image in Fig. 1 for the upper layer of the defect core compared with simulated ones from Humble models A and D. DFT-calculated atomic coordinates are shown as black and red dots for models A and D, respectively, at the bottom. (b) Experimental atomic coordinates from 2D Gaussian fitting of the HAADF images in Fig. 1 compared with DFT-relaxed Humble model A.

Figure 4

Si percentage of SiGe pillars near the Humble defect. EELS line profiles of Si content across the defect in the area shown on the right. Same information for a SiGe pillar without the defect is shown in comparison. Scale bar: 2 nm.