Ge–Si–O phase separation and Ge nanocrystal growth inGe:SiOx/SiO2 multilayers—a new dc magnetron approach

Abstract

Ge:SiOx/SiO2 multilayers are fabricated using a new reactive dc magnetron sputtering approach. Theinfluence of the multilayer stoichiometry on the ternary Ge–Si–O phase separation and thesubsequent size-controlled Ge nanocrystal formation is explored by means ofx-ray absorption spectroscopy, x-ray diffraction, electron microscopy and Ramanspectroscopy. The ternary system Ge–Si–O reveals complete Ge–O phase separation at400 °C which does not differ significantly to the binary Ge–O system. Ge nanocrystals of < 5 nm size are generated after subsequent annealing below700 °C. It is shown that Ge oxides contained in the as-deposited multilayers are reduced by asurrounding unsaturated silica matrix. A stoichiometric regime was found where almost noGeO2 is present after annealing. Thus, the Ge nanocrystals become completely embedded ina stoichiometric silica matrix favouring the use for photovoltaic applications.