Raman scattering from quantum dots of Ge embedded in SiO2 thin films

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Abstract
Raman measurements were carried out on Ge quantum dots from 6.1 to 15 nm in size embedded in SiO2 thin films. The samples were prepared by rf co‐sputtering and post‐ annealing. In contrast to the amorphous‐like broad spectra previously obtained for gas‐ evaporated Ge microcrystals of comparable sizes, relatively sharp lines around 300 cm−1 were observed, because the present dots satisfy the fixed boundary condition. The increase in the linewidth observed with decreasing the size is in good agreement with the results of the calculation based on the phonon confinement model. However, the downward shift of the line predicted from the calculation was not observed presumably due to the compressive stress exerted on the dots.