Growth and characterization of Ge nanocrystals in ultrathin SiO2 films

Ge nanocrystals embedded in SiO2 glassy matrices have been formed by the deposition of a Ge film on a SiO2 layer and the subsequent thermal oxidation of the structure at a temperature between 8008C and 10008C. Secondary ion mass spectrometry SIMS.results indicate that the Ge precipitates into the bulk SiO2 at a density of 1=1012 cmy2. Raman spectra show a sharp peak at 300 cmy1 for the nanocrystallized Ge. The average radius of the Ge nanocrystals in SiO2 was determined to be about 5 nm by means of analysis of Raman spectra. In the metal-insulator-semiconductor MIS.structure, electron storage occurs in the SiO2rGerSiO2potential well via electron tunneling into the oxide film. Capacitance–voltage C–V.measurements indicate that the flatband voltage VFB.shifts to 0.91 V after the electron injection. The VFB 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 SiO2rGerSiO2structure. q1998 Elsevier Science B.V. All rights reserved