Cross-sectional transmission electron micrographs of a fully coalesced Ge film (a) without annealing during islands stage of growth and (b) with island annealing. Image (a) shows the high density of twin/stacking fault defects emanating from the Ge-Si-SiO2 interface. Image (b) shows the existence of threading dislocations at the interface.
Scanning electron micrographs of Ge islands deposited within openings in chemical SiO2. Images (a)—(d) have initial amounts of 8, 12, 18, and 25 nm of Ge deposition. The images track the coalescence and morphology of the islands with increasing deposition. Higher magnification images, as shown in the insets of (a) and (b), are used to estimate the amount of Ge contained within the islands based on the average island density and diameter.
Image (a) is a high-resolution cross-sectional transmission electron microscope image of the sample with 12 nm of Ge deposition, where the Ge islands have just begun to coalescence. The Ge island on the right is nucleated in a twin relationship to the Si and has formed a coherent twin boundary at the junction with the epitaxial Ge island on the left. The twin boundary is magnified in the filtered image that is inset where the islands have merged. The diffraction patterns of the islands and substrate are also included as insets. Image (b) is a schematic drawing of the orientation of the islands corresponding to the image in (a).
Scanning electron micrographs of Ge islands after annealing with initial deposition of 8, 12, 18, and 25 nm, images (a)—(d), respectively. The islands density is reduced by a factor of 16 after annealing. Images (c) and (d), and insets therein, also show the formation of very large Ge islands surrounded by trenches that extend down into the Si. The density of the large islands is the same in both images.
Cross-sectional transmission electron microscope images of the annealed islands with 8 nm of initial Ge deposition. Image (a) is a low-resolution image showing the morphology of the surface. Images (b)—(e) are high-resolution images of the islands 1 through 4 shown in image (a). The islands rest upon a Ge-Si alloy layer and are slightly misoriented with respect to the Si substrate.
High-resolution cross-sectional transmission electron microscope image of island number 4, from Fig. 3(a). This island is found to possess a small angle tilt boundary with the Si with an edge dislocation spacing of 5 nm. The numbered regions correspond to locations where the composition is measured using energy dispersive spectroscopy.
(Color) Strain analysis of the image shown in Fig. 6 using geometric phase analysis. Image (a) shows the geometric phase of the (111) lattice fringes with a 2 nm spatial resolution. Images (b) and (c) show the resulting ɛ xx and ɛ yy strain maps of Fig. 6 relative to the Si region marked by the dashed square in (b). Image (d) shows a plot of the ɛ xx strain profiles averaged over 20 nm along the interface for the solid and dot-dashed lines marked in (b).
Cross-sectional transmission electron microscope image of large Ge island that forms after annealing the sample with 25 nm of initial Ge deposition. The island is epitaxially oriented to the Si and contains threading dislocations. The trench that extends down into the Si is shown to the right of the island.
Cross-sectional transmission electron microscope image of Ge islands with 25 nm of initial Ge deposition. The islands are then capped with spin-on-glass and then annealed. Stacking faults and twin defects remain within the islands, and their morphology is unchanged from the pre-annealed state. The chemical SiO2 layer is also preserved during annealing. The inset shows a close-up view of one of the islands and reveals the GeSi alloy layer formed beneath the island.
(Color online) Depiction of the evolution of the Ge islands during annealing. Image (a) shows the nucleation of the Ge islands within the openings in SiO2. The cross hatch island indicates a tilt misorientation with respect to the Si substrate. Annealing causes desorption of the SiO2 layer. Image (b) represents the surface diffusion that takes place from the epitaxial Ge islands to the exposed Si substrate as well as interdiffusion of Si and Ge. Ge also migrates by surface diffusion to the misoriented island. Image (c) shows the growth of the misoriented islands and the larger Ge-Si alloy layer that forms beneath the island.
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