Dielectric function of germanium nanocrystals between 0.6 and 6.5 eV by spectroscopic ellipsometry

In this work, we report on the study of dielectric function of nanocrystalline germanium (nc-Ge) implanted in a host matrix SiO2 on a silicon substrate by spectroscopic ellipsometry (SE). The presence of nc-Ge is observed by transmission electron microscopy (TEM). The SE measurements are performed at 70° of angle of incidence in air at room temperature.We observe that the ellipsometric angles ψ and Δ change under specific conditions of elaboration. The dielectric function of germanium nanocrystals ɛnc-Ge is extracted using wavelength by wavelength inversion method, without any dispersion law or adjustment parameters. The critical points are determined from the second derivative of the imaginary part of the dielectric function. As expected the significant broadening of the critical points is observed, the E0, E1, E1+Δ   and E0′ critical points shift to higher energies, affected by quantum confinement. This implies a significant change in the direct and indirect transitions responsible for the band structure.