Photoluminescence study of Ge nanocrystals irradiated by reactor neutron flux

Samples of Ge nanocrystals (Ge-ncs) embedded in amorphous SiO2 film were prepared by Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor followed by the second annealing. Irradiation with thermal neutrons leads to doping of nanocrystals with Ga, As and Se impurities due to nuclear transmutation of isotope 70Ge into 71Ga, isotope 74Ge into 75As, isotope 76Ge into 77Se, respectively (neutron transmutation doping, NTD). Irradiation with fast neutrons leads to appearance of radiation damages, which are expected to be removed after the second annealing. Photoluminescence (PL) measurements show that PL is quenched after neutron irradiation, and restored after annealing higher than 500 °C. The PL spectra of doped Ge-ncs samples show more intense exciton radiative luminescence than of undoped Ge-ncs sample, which is related to that the donor and acceptor impurities recombine the nonradiative centers in the interface of Ge-ncs and SiO2 matrix, and enhance the probability of exciton recombination.