Properties of Ge nanocrystals formed by implantation of Ge+ ions into SiO2 films with subsequent annealing under hydrostatic pressure

The influence of hydrostatic compression on the implantation-induced synthesis of Ge nanocrystals in SiO₂ host was studied. It is found that high-temperature annealing under pressure leads to retardation of Ge diffusion in SiO₂. It is shown that unstressed Ge nanocrystals are formed as a result of conventional annealing (under atmospheric pressure). Annealing under pressure is accompanied by formation of hydrostatically stressed Ge nanocrystals. The stress in Ge nanocrystals was determined from optical-phonon frequencies in the Raman spectra. The shift of Raman resonance energy (E₁, E₁ + Δ₁) corresponds to the quantization of the ground-state energy for a two-dimensional exciton at the critical point M₁ of germanium. It is ascertained that a photoluminescence band peaked at 520 nm is observed only in the spectra of the films which contain stressed Ge nanocrystals.