Strain-induced direct band gap shrinkage in local Ge-on-insulator structures fabricated by lateral liquid-phase epitaxy

Direct band gap shrinkage in Ge-on-insulator (GOI) structures fabricated by lateral liquid-phase epitaxy (LLPE) was investigated by means of micro(μ)-photoluminescence and μ-Raman spectroscopy. The LLPE method, based on the rapid thermal process, was found to be an effective and feasible way to produce highly strained local GOI structures. We observed a significant redshift of direct gap emission amounting to 45 meV from the tensile-strained GOI layer. Strain analysis and temperature dependent PL spectra indicated that a direct band gap shrinkage was mainly due to a tensile strain of about 0.4% induced by rapid crystallization from the Ge melting point during the LLPE process. The local optical properties along the LLPE-grown GOI wire were examined and discussed on the basis of μ-PL mapping images.