The effect of rapid thermal annealing temperature on the diffusion of silicon (Si) and germanium (Ge) and the formation of Ge nanocrystals in a silicon oxide matrix was investigated. The formation of Ge nanocrystals was attributed mainly to the reduction of Ge suboxides by Si diffused from the Si substrate. For samples annealed at 800°C, the nanocrystals were uniform in size and distributed evenly in the bulk of the oxide but became denser nearer to the silicon–silicon oxide (Si–SiO2) interface. When the sample was annealed at 900°C, two regions with different nanocrystal densities and size distributions separated by a region void of nanocrystals were observed. The region of denser nanocrystals was located near the Si–SiO2 interface. For annealing at 1000°C, nanocrystals were only observed at the Si–SiO2 interface and these have significant size variation, with the rest of the oxide being void of nanocrystals. The nanocrystals formed at 900 and 1000°C were generally found to be defective.

Ge nanocrystals embedded in lanthanide-based high-k dielectric ͑amorphous Lu 2 O 3 in this work͒ were formed using pulsed laser deposition followed by rapid thermal annealing in N 2 ambient. The formation and evolution of the Ge nanocrystals have been studied using transmission electron microscopy ͑TEM͒, x-ray photoelectron spectroscopy ͑XPS͒ in conjunction with depth profiling, and secondary ion mass spectroscopy ͑SIMS͒ analysis. Plan-view TEM images indicated that the formation of nanocrystals was first initiated during the deposition process. The annealing treatment significantly enhanced the nucleation of Ge nanocrystals, resulting in a high areal density of 7 ϫ 10 11 cm −2 Ge nanocrystals with a mean size of about 6 nm in diameter in the amorphous Lu 2 O 3 matrix. XPS depth profile analysis revealed that Ge nanocrystals were predominantly formed from the precipitation of Ge nuclei from the oxide phase. A low annealing temperature of 400 °C was sufficient to dissociate the GeO 2 and GeO x leading to the formation of Ge nanocrystals. An accumulation of Ge species close to the upper Ge/ Lu 2 O 3 interface was observed from XPS and SIMS depth profile analysis. Different charge storage behaviors observed from the memory capacitor devices before and after annealing could be correlated to the changes in structure and composition of the film. The memory capacitor device fabricated from the annealed sample showed efficient charge storage effect under a low operation voltage without significant initial charge decay.