Strain Relaxation In Islands Research Articles

Atomic scale study of strain relaxation in Sn islands on Sn-induced Si(111)-(23×23) surface

Surface structure of the Sn islands 5 ML high, prepared on Si(111)-(23×23)-Sn substrate, is investigated by low temperature scanning tunneling microscopy/spectroscopy. Due to the elastic strain relaxation in the islands, the in-plane unit cell structure distorts and the apparent height of the surface atoms varies regularly to form an overall modulated strip structure. The quantum well states are observed to depend on the relative position within this structure, which implies the change of the surface chemical potential induced by the elastic strain relaxation as well.

Molecular dynamics study of dislocation formation in a [001] face-centered-cubic epitaxial island under tensile stress

Dislocation formation in homoepitaxial pyramidal [001] Cu islands under tensile stress is studied using molecular dynamics simulations. It is found that 90° Shockley partial dislocations are dominant in the island strain relaxation. For a low-aspect-ratio island, the dislocations are nucleated from the island surface and propagate downwards to form misfit dislocations. For a high-aspect-ratio island, a pair of the dislocations on the same slip plane are simultaneously nucleated respectively from the two island edges, propagate inwards, and react to form a 90° Shockley misfit partial dislocation. These dislocations can form sequentially and cooperatively.

Structural and optical properties of vertically correlated Ge island layers grown at low temperatures

We studied the vertical correlation of small hut-like Ge islands in Si–Ge multilayers grown by molecular beam epitaxy (MBE) at 510 °C in the modified Stranski–Krastanov growth mode. The fundamental, structural and optical properties of stacked Ge islands embedded in Si are analyzed by in-situ RHEED, TEM, photoluminescence (PL), and photocurrent (PC) spectroscopy. Ge islands of about 20 nm width and 2 nm height reveal a reduction in the critical Ge coverage for correlated growth for Si spacer widths below about 14 nm. This value is much smaller than observed for dome-like islands of about 80 nm size deposited at higher temperatures. Such a scaling of island separation for stacked growth with island diameter is suggested by finite element simulations of elastic strain relaxation in islands. The correlation affects island size, island density, and local strain fields which may have a direct impact on band offsets and the electronic coupling of stacked islands. This is important for possible application in devices like NIR Si–Ge dot photodetectors and tunneling structures.