SELF-FORMATION OF GERMANIUM NANOCRYSTALS AND ITS APPLICATION TO SELF-ADAPTIVE NEURAL DEVICES

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Metal-oxide-semiconductor (MOS) structures with a Ge nanocrystal embedded in SiO_2 films were fabricated by Ge^+ ion implantation and subsequent high-temperature annealing. The Raman spectra indicate the evidence of self-assembled Ge nanocrystals in the SiO_2 films. The Ge size and its density were estimated to 3-5 nm and 1×10^<12>/cm^2, respectively. Photoluminescence spectra showed a strong blue-violet band around 400 nm and a weak near-infrared band around 750 nm, respectively. The several implantation-induced deficient centers are believed to be responsible for the blue-light luminescence. Capacitance-voltage characteristics exhibit the flat-band voltage shifts of 1.02 V after the electron injection into the SiO_2/Ge/SiO_2 potential well. An anomalous leakage current was clearly observed in the current-voltage characteristics. The precise simulation of quantum electron transport in the SiO_2 film indicates that the anomalous conduction is originated from resonant tunneling in the SiO_2/Ge/SiO_2 double-well band structure.