Isoelectronic hydrogen-related defects in silicon
We report data for two hydrogen-related radiation-damage centres, known as the and centres, and compare their properties with the other `B' centres in silicon. We show that the radiative lifetimes of the luminescence are long, for the centre at 6.5 K and for the centre at 2 K, consistent with the luminescence occurring from excitons bound to centres which are isoelectronic with the silicon lattice. The energies of the bound-exciton multiplet states and their response to magnetic fields can be fitted precisely when the primary axis of each centre is close to a axis in the silicon. The excitons have spectroscopic binding energies of 12 and 18 meV for the two centres. However, the vibronic sidebands indicate that relaxations of meV occur when the excitons are bound. The centres are thus excellent examples of defects whose excited states are resonant with the crystal band states until stabilized by the relaxation. Comparison of the properties of the known shallow hydrogen-related radiation-damage centres in silicon shows that they form a unified class of similar defects.