Optical transitions in Ge nanocrystals formed by high-pressure annealing of Ge~+ ion implanted SiO_2 films

摘要

Optical transitions in Ge nanocrystals formed by high-pressure annealing of the Ge~+ ion implanted SiO_2 films have been studied by Raman and photoluminescence spectroscopy. It has been found that the E_1,E_1 + Δ_1 Raman resonance shift observed from the unstrained and bydrostatically compressed nanocrystals corresponds to the quantization of the electron-hole state spectrum of the Ge band. It has also been established that the appearance of a green photoluminescence band centered at 420-520 nm correlates with the formation of strained nanocrystals. Comparisons of the PL data with HRTEM results have been made, which suggest that the green PL arises from strained Ge nanocrystals of a radius of less than 5 nm. The direct electron-hole recombination at Γ is discussed as a possible origin of the observed photoluminescence band.