Optical properties of spark-processed Ge

We report the photoluminescence (PL) and decay times of spark-processed Ge (sp-Ge) at various temperatures. Further Fourier transform infrareds (FTIR) have been measured. The luminescence peak of sp-Ge is observed around 520 nm with two new shoulder peaks at 410 and 610 nm at room temperature. At low temperature, however, two shoulder peaks become dominant while the green luminescence peak vanishes. Moreover, the PL peak wavelength remains constant during cooling. The decay times are characterized as a fast decay time of a few tens of ns and slow decaying tails in μs range and independent of measured wavelengths. Further, low temperature luminescence measurements for three luminescence bands of sp-Ge reveal a considerable degree of local disorder. Vibrational modes obtained from FTIR are mainly composed of GeO modes with some OH vibration. These results suggest that the origin of PL from sp-Ge is associated with GeO related defects rather than the radiative recombination of excitons confined in nanocrystals.