Structural and electrical properties of sol–gel derived Ge nanocrystals in SiO2 films

Stoichiometric mixed germanate–silicate glass films were fabricated on boron-doped silicon substrates by means of a sol–gel based synthesis procedure. In order to initiate the growth of elemental germanium (Ge) nanocrystals, the glass films were annealed in forming gas at temperatures between 600 and 1000°C. High-resolution and conventional transmission electron microscopy show that the shape and size of Ge nanocrystals embedded in the glass film are strongly influenced by the annealing conditions. Energy-dispersive X-ray analysis reveals that Ge segregates at the interface to the silicon substrate and evaporates from the free surface. This leads to a denuded zone of Ge nanoparticles close to the Si substrate and the SiO2 surface. Capacitance–voltage measurements of a metal–oxide–semiconductor structure with and without Ge particles demonstrate the charge-storage characteristic of the thin-layer structure. We identify clear trends in the electrical properties of the nanoparticles as a function of the annealing conditions and observe correlations between trapped charge and particle density.