Stress transition from compressive to tensile for silicon nanocrystals embedded in amorphous silica matrix

• Silicon-rich silicon oxide films were deposited and annealed at 1100 °C.
• Quantum and phonon confinement effects were investigated for silicon nanocrystals.
• It was found that size-dependent stress is exerted on the nanocrystals.
• Stress transition from compressive to tensile was discovered and discussed.

Silicon-rich silicon oxide films, with various Si concentrations, were deposited by plasma enhanced chemical vapor deposition and annealed at 1100 °C in order to form silicon nanocrystals. For these films, it has been found that the absorption edge shifts as a function of the nanocrystal size due to the quantum confinement of exciton. This result showed that the size-related effects are present in the investigated films. Next, we examined the influence of the nanocrystal size on the vibrational modes. In this case, the Raman line related to silicon nanocrystals significantly down-shifts as a function of the nanocrystal size, which is against the predictions of the phonon confinement model. It has been shown that this effect is due to stress exerted on the nanocrystals. It has been also found that this stress changes from compressive to tensile, and the stress character depends on the film stoichiometry.