Synthesis and Characterization of Ge Nanoclusters in Amorphous GeOx(x∼0.1) Nano-Films Grown by Magnetron Sputtering

We investigated how the processing condition of the amorphous Ge (
$\alpha-\text{Ge}$
) nano-films (growth technique, substrate temperature, annealing conditions and the processing atmosphere composition) influence on their physical-chemical properties. Ge clusters or quantum dots (QDs) in
$\alpha-\text{Ge}$
nano-films were prepared by a combined process comprising the magnetron sputtering technique and a post-grown annealing stage at 800 K for 3.5 hours in a reducing atmosphere. The
$\alpha$
-Ge nano-films were grown in the temperature range from 300 to 800 K. Secondary ion mass spectrometry (SIMS) analysis shown an oxygen content of
$3.5\times 10^{21}\ \text{cm}^{-3}$
in the films fixed by operative conditions of the sputtering system. The electrical characterization shown that the samples grown at room temperature resulting insulating, while the samples grown at temperatures over 500 K have n-type conductivity with electron concentration of
$3.5\times 10^{19}\ \ \text{cm}^{-3}$
, in average. The optical transmittance and photoluminescence characterization demonstrated that the films have an optical bang gap (Eg) of 1.2
$\text{eV}$
, generated by the presence of Ge nanoclusters in the
$\alpha-\text{GeO}_{\mathrm{X}}$
nano-films. The process used in this work demonstrated their potential to nucleate Ge clusters with sizes from 1 to 8 nm in an amorphous matrix, as was proven by X-ray diffraction (XRD) and Raman scattering measurements.