The processes of erbium impurity excitation in Si/Si1−xGex:Er/Si heteroepitaxial structures

We report a study into the photoluminescence excitation spectra of Er3+ ions in Si/Si1−xGex:Er/Si heteroepitaxial structures containing 10-31% germanium. The structures of this type are of interest for a laser realization on Si basis. It is shown that a characteristic maximum in the 1040-1050 nm region that appears in these structures is related with the backscattering effects of radiation in the silicon substrate. The excitation efficiency of Er impurity in Si/Si1−xGex:Er/Si structures is investigated in conditions of band-to-band and sub-bandgap optical pumping with the photon energies smaller than the bandgap of a Si1−xGex solid solution. The effective excitation cross-section of erbium ions is shown to depend on the excitation mechanism, the excitation energy, and the parameters of Si1−xGex:Er layers. The values of the effective excitation cross-section of Er3+ ions in Si/Si1−xGex:Er/Si structures were found to vary from 4 × 10−15 to 0.5 × 10−16 cm2 at T = 77 K. These values are comparable with the highest values obtained for the excitation cross-section of Er3+ ions in silicon and exceed by several orders of magnitude the effective cross-section of Er3+ ions under direct (intra-atomic) excitation.