Effect of Ge doping on the creation of luminescent radiation defects in MBE Si

We report on the observation of new luminescence centres in irradiated Ge-doped Si (Si:Ge). Molecular beam epitaxy grown Si:Ge samples with Ge content in the range 0-1.25 at.% were irradiated with protons at room temperature and subjected to post-irradiation heat treatments at temperatures from 100 to 650 °C. For each annealing step, the samples were investigated by means of photoluminescence (PL) spectroscopy at temperatures between 4 and 300 K. We have found that the PL spectra of Ge-containing samples are different from those measured in Ge-free samples and from those previously reported in irradiated bulk Si:Ge. Several new lines have been found in the near band edge (NBE) region of the spectrum, whereas many lines typically measured in Ge-free irradiated Si have not been observed. The dependence of the intensity of the new NBE lines on the measurement temperature has been studied. With increasing Ge content, these lines shift to lower energies following the band gap shrinkage. However, they are broader than expected, when only a purely statistical variation of the band gap energy produced by local fluctuations in the alloy composition is taken into account.