Band-to-band radiative transitions in germanium thin films deposited on silicon were analyzed, and compared with those in bulk material. A significant down-shift of the direct transition-related peak was observed from the thin films samples, caused by the preparation-generated tensile strain in the film. A comparison of the ratios of the direct to indirect transition peak intensities showed that those were very similar for the thin films and the bulk material, when the self-absorption of the emission was accounted for. The observed similarity in the spectral shape indicated that the strong direct transition luminescence detected in strained germanium films was mainly due to the improved light extraction in the energy range of about 0.8eV, rather than an increase in the probability of band to band direct transition. A feature was found, at around 0.72eV in the spectrum of the germanium luminescence, which correlated with the presence of dislocations in the crystal. The origin of this feature was considered in terms one dimensional dislocation bands, split off from the Gamma valley of the conduction band due to the dislocation local strain field.

Room Temperature Luminescence from Germanium. T.Arguirov, M.Kittler, N.V.Abrosimov: Journal of Physics - Conference Series, 2011, 281[1], 012021