Growth and characterization of Ge nanocrystals in ultrathin SiO 2 films

Abstract

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°C and 1000°C. Secondary ion mass spectrometry (SIMS) results indicate that the Ge precipitates into the bulk SiO 2 at a density of 1×10 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 nm 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.