Ge nanoparticle formation by thermal treatment of rf-sputtered ZrO2/ZrGe2O3 superlattices

ZrO2/ZrGe2O3 superlattices were deposited on Si wafers and thermally treated at different temperatures to form Ge nanocrystals embedded in a ZrO2 matrix. The formation process of Ge nanocrystals has been investigated by means of methods like Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. With increasing temperature, there is first a separation process leading to flat Ge clusters between amorphous ZrO2 layers and then at about 630 °C a crystallization process of both the Ge clusters and the ZrO2 layers starts simultaneously. An orientation relation of the Ge and ZrO2 nanocrystals could be proven by high-resolution transmission electron microscopy.