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

Knebel S, Kyriakidou A, Bracht H, Rösner H, Wilde G

Zusammenfassung

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 1000A degrees 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 SiO(2) 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.