RBS depth profiling and optical characterization of multilayers of TiO2 (20 nm) and Ge (15 nm)

Rutherford Backscattering Spectrometry (RBS) has been employed for studying inter-layer diffusion and mixing of TiO2 and germanium in the multi-layers grown on the soda lime glass substrate. TiO2 layers were grown by electron-beam evaporation of titanium in an oxygen atmosphere and Ge layers were grown by resistive heating. UV–visible and Raman spectroscopy were carried out for optical characterization. RBS spectra were analyzed by SIMNRA which confirmed the successful formation of alternate layers of TiO2 and Ge with a thickness of 20 nm and 15 nm, respectively. Annealing caused interface mixing. The approximate stoichiometry of interfaces was of GeTiO2. The thickness of these layers increased with annealing temperature. Two to five top Ge layers also underwent oxidation to form GeO and GeO2, depending on annealing temperature. Nuclear Reaction Analysis (NRA) signal of oxygen from top layers was also recorded to confirm the pick-up of oxygen from the annealing atmosphere. An increase in the transmission efficiency with blue shift of the absorption edge was also observed with annealing temperature, as associated with the decrease in the effective thickness of Ge layers. Shift of Raman peaks confirmed the stoichiometric changes as a result of annealing.

► Multilayers of TiO2 (20 nm) and Ge (15 nm).
► RBS depth profiling.
► Effects of annealing.
► Inter-layer diffusion and various degrees of oxidation of Ge layers.
► Enhancement of quantum confinement effects and changes in optical properties.