Growth and characterization of Ge nanocrystals in ultrathin SiO2 films

Ge nanocrystals embedded in SiO(2) glassy matrices have been formed by the deposition of a Ge film on a SiO(2) 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 indicate that the Ge precipitates into the bulk SiO(2) at a density of 1 x 10(12) cm(-2). Raman spectra show a sharp peak at 300 cm(-1) for the nanocrystallized Ge. The average radius of the Ge nanocrystals in SiO(2) was determined to be about 5 Mm by means of analysis of Raman spectra. In the metal-insulator-semiconductor (MIS) structure, electron storage occurs in the SiO(2)/Ge/SiO(2) potential well via electron tunneling into the 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 electron 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 attributed to resonant tunneling in the SiO(2)/Ge/SiO(2) structure. (C) 1998 Elsevier Science B.V. All rights reserved.