Formation and optical properties of Ge films grown on Si(1Â 1Â 1) substrates using nanocontact epitaxy

Ge thin films were epitaxially grown on Si(1 1 1) substrates using ultrathin SiO2 film technique called nanocontact epitaxy. The key to this technique was the use of high density spherical nanodots (NDs) as seed crystals for the epitaxial growth of the Ge films. The seed crystal NDs were elastically strain-relaxed without misfit dislocations so that highly crystalline Ge thin films could be formed. The Ge films were ≈140 nm in thickness and were composed of island-shaped domains with flat Ge(1 1 1) surfaces. The domains had an average size of ≈1 μm and flat surfaces with root mean square of a surface roughness of ≈3 nm. The films had a photoluminescence peak at 0.8 eV, which meant that the films were highly crystalline.