Ge nanocrystals embedded in a SiO2 matrix obtained from SiGeO films deposited by LPCVD

Abstract

SiGeO films were deposited by LPCVD using Si2H6, GeH4 and O2 as reactive gases and furnace annealed to segregate the excess of Ge in the form of nanocrystals embedded in a SiO2 matrix in a low temperature budget process fully compatible with current processing technologies. For low GeH4 partial pressures (4.8 mTorr) and a deposition temperature of 450 °C, the deposited film consists of a SiO2 matrix incorporating Ge atoms, and no Ge oxides are detected. After annealing of the sample at a temperature of 600 °C, quasi-spherical isolated Ge nanocrystals homogeneously distributed throughout the whole film thickness, with diameters ranging from 4.5 to 9 nm and an areal density of around 7 × 1011 cm−2, are formed while the SiO2 matrix holds its original composition. Increasing the GeH4 partial pressure results in only a slight increase in the density of nanoparticles with no significant changes in their diameters and a matrix is formed by a mixture of Si and Ge oxides. A decrease in the deposition temperature results in very slow growth rates. Finally, increasing the annealing temperature causes no improvement in the sample characteristics, but a transformation of the matrix into a mixture of Si and Ge oxides takes place and Ge diffusion processes start to appear.