GROWTH AND CHARACTERIZATION OF GE NANOCRYSTALS IN ULTRATHIN SIO2-FILMS

Ge nanocrystals embedded in SiO2 glassy matrices have been formed by t he deposition of a Ge film on a SiO2 layer and the subsequent thermal oxidation of the structure at a temperature between 800 degrees C and 1000 degrees C. Secondary ion mass spectrometry (SIMS) results indicat e that the Ge precipitates into the bulk SiO2 at a density of 1 x 10(1 2) cm(-2). Raman spectra show a sharp peak at 300 cm(-1) for the nanoc rystallized Ge. The average radius of the Ge nanocrystals in SiO2 was determined to be about 5 Mm by means of analysis of Raman spectra. In the metal-insulator-semiconductor (MIS) structure, electron storage oc curs in the SiO2/Ge/SiO2 potential well via electron tunneling into th e oxide film. Capacitance-voltage (C-V) measurements indicate that the flatband voltage (V-FB) shifts to 0.91 V after the electron injection . The V-FB Shift is attributed to the charge storing for a single elec tron per potential well. A step was observed in the current-voltage (I -V) characteristics. The precise simulation of quantum transport in a quantum size structure indicates that the step in the I-V curve is att ributed to resonant tunneling in the SiO2/Ge/SiO2 structure. (C) 1998 Elsevier Science B.V. All rights reserved.