Fabrication of multilayered Ge nanocrystals by magnetron sputtering and annealing

Abstract

Multilayered Ge nanocrystals embedded in Si and Ge oxide films have been fabricated on Si substrateby a (SiO2+Ge)/(SiO2+GeO2) superlattice approach, using an rf magnetron sputtering technique with aGe+SiO2 composite target and subsequent thermal annealing inN2 ambientat 750 °C for 5 min. X-ray diffraction (XRD) measurements indicated the formation of Genanocrystals with an average size estimated to be 9.8 nm. Raman scatteringspectra showed a peak of the Ge–Ge vibrational mode shifted downwards to298.8 cm−1, which was caused by quantum confinement of phonons in the Ge nanocrystals. X-rayphotoemission spectroscopy (XPS) analysis demonstrated that the Ge chemical state is mainlyGe0 in the(SiO2+Ge) layerand Ge4+ in the (SiO2+GeO2) layer in the superlattice structure. Transmission electronmicroscopy (TEM) revealed that Ge nanocrystals were confined in(SiO2+Ge) layers, and had good crystallinity. This superlattice approach significantly improved boththe size uniformity of Ge nanocrystals and their uniformity of spacing on the‘Z’ growth direction compared with the conventional Ge-ncs fabrication method using a single and thickSiO2 matrix film.