Self-assembled germanium nano-structures by laser-assisted oxidation

The investigation on the oxidation behaviour of Si$_{1-x}$Ge$_{x}$ alloys($x$=0.05, 0.15, and 0.25) is carried out. It is found for the first time thaton the oxide film a germanium nano-cap with a thickness of 1.8--2.8nmand a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm areformed by the low-temperature laser-assisted dry oxidation of Si$_{1 -x}$Ge$_{x}$ substrate. A new scanning method on the decline cross-section ofthe multiple-layer sample is adopted to measure the layer thickness and thecomposition. Some new peaks in photoluminescence (PL) spectra arediscovered, which could be related to the nano-cap and the nano-particles ofgermanium. A suitable model and several new calculating formulae with theunrestricted Hartree--Fock--Roothaan (UHFR) method and quantum confinementanalysis are proposed to interpret the PL spectra and the nano-structuremechanism in the oxide.