Optical properties of a silver-related defect in silicon

Doping crystalline silicon with silver results in a photoluminescence center with multiplet zero-phonon structure near 778.9 meV. We show that the published assignments of the vibronic sidebands are wrong, with severe implications for the relative transition probabilities of the luminescence transitions from the excited states. At low temperature, most of the luminescence intensity derives from the phonon sideband associated with a forbidden zero-phonon line through the phonon-assisted coupling of two of the excited states of the center. The effective mass of the vibration is determined from isotope effects to be close to the mass of one Ag atom. Uniaxial stress and magnetic perturbations establish that the current assignment of the electronic structure of the center is incorrect and that it is best described by a new variant on the "pseudodonor" model. An electron orbits in an effective T-d environment, with an orbital triplet as its lowest-energy state, giving a j=3/2 electron state. A tightly bound hole has its orbital angular momentum quenched by the C-3v symmetry of the center, leaving only spin angular momentum (s=1/2). These particles couple to give J=2,1,0 states. Using this model, the temperature dependence of both the total luminescence intensity and measured radiative decay time can be understood. These data allow an estimate to be made of the thermally induced transition rate of the electron from the effective-mass excited states into the conduction band.