Formation of Ge nanocrystals and evolution of the oxide matrix in as-deposited and annealed LPCVD SiGeO films

SiGeO films were deposited by LPCVD using Si2H6, GeH4 and O2 as reactive gases and furnace annealed to segregate the possible excess of Si and Ge in the form of nanocrystals embedded in an oxide matrix. For low GeH4:Si2H6 flow ratios and deposition temperatures of 450 ∘C or lower, the deposited film consists of a SiO2 matrix incorporating Ge. No Ge oxides and no nanocrystals are detected. After annealing of the samples with SiO2 matrices at temperatures of 600 ∘C or higher, quasi-spherical isolated Ge nanocrystals with diameters ranging from 4.5 to 9 nm and homogeneously distributed throughout the whole film thickness are formed. In the samples deposited with low GeH4:Si2H6 flow ratios, the original SiO2 matrix holds its composition.