Influence of the deposition and annealing temperatures on the luminescence of germanium nanocrystals formed in GeO$_{x}$ films and multilayer Ge/SiO$_{2}$ structures

The GeO$_{x}$ films and multilayer nanoperiodic Ge/SiO$_{2}$ structures containing germanium nanocrystals were prepared by physical vapor deposition in vacuum. The properties of the films and multilayer structures were controlled by varying the deposition temperature in the range of 35–590$^\circ$C and the annealing temperature in the range of 400–1000$^\circ$C. A comparative study of the optical and structural characteristics of the nanosystems was performed using the methods of Raman scattering spectroscopy, IR spectroscopy, photoluminescence, and electron microscopy, which demonstrated a qualitative similarity of the nanosystems. It was found that annealing at temperatures in the range of 600–800$^\circ$C leads to the formation of germanium nanocrystals with a high density ($\sim$10$^{12}$ cm$^{-2}$), whereas in the materials not subjected to annealing, their density did not exceed $\sim$10$^{10}$ cm$^{-2}$. The average size of the nanocrystals was found to be 5 $\pm$ 2 nm. For both nanosystems, three luminescence bands were observed at 1.2, 1.5–1.7, and 1.7–2.0 eV. It was assumed that the origin of these bands is associated with germanium nanocrystals, oxygen-deficient centers in GeO$_x$, and defects at the Ge/dielectric interface, respectively.