Properties of unstable donors generated in Si during laser irradiation

The generation of unstable at room temperature centers in boron-doped Si during laser annealing are under investigation. It is shown, that the generation of two kinds of unstable centers with different recombination time constants during the laser annealing takes place. Through an investigation of dependence of the recombination time constants on temperature the activation energies of these donors are determined: EF equals 0.8 - 0.9 eV and E2 equals 1.4 - 1.5 eV. It is detected, that recombination time constants of centers depend on boron and oxygen atoms concentrations in laser-annealed region -- recombination time constants of both kinds of centers decrease with increase of both boron and oxygen concentrations in silicon. It is shown, that the generation of these unstable donors does not occur during the laser annealing of boron-doped silicon with basic frequency of Q-switched Nd:YAG-laser (wavelength 1.06 micrometer). The model of generation mechanism of the donors is proposed taking into account dependence of recrystallization velocity during pulsed laser annealing on absorption coefficient of radiation and a great difference in absorption coefficients of basic (k1 equals 15 cm-1) and double (k2 equals 104 cm-1) frequencies of Nd:YAG-laser radiation.