Luminescence centres containing two, three and four hydrogen atoms in radiation-damaged silicon

Photoluminescence measurements are reported which show that the centres responsible for the X-lines, which are created by radiation damage in silicon deliberately doped with hydrogen followed by annealing at 450°C, contain two, three or four hydrogen atoms at equivalent or inequivalent sites. The large hydrogen-deuterium isotope shifts observed are shown to be caused primarily by linear electron-phonon coupling and the anharmonicity of local vibrational modes. There is negligible interaction between different hydrogen atoms within each centre and the isotope shifts associated with different sites in a centre can have opposite signs.