A photoluminescence study of selenium-diffused silicon

Abstract

Two optical bands due to short-time diffusion of Se in Si have been studied by a photoluminescence technique. The bands show similarities to the two Se-related bands reported previously but have shifted in energy. The Se-related bands reported here are only observed after short-time diffusion and, e.g., they are observed after 9 min but not for 18 min diffusion at 1100 °C. One of the bands consists of three sharp zero-phonon lines whereas the other one only shows broad structures. A thermalization study indicates that the sharp lines are due to spin-singlet and -triplet initial states similarly to the Se and S bands studied previously. The spin-triplet state appears to be split into three components which is interpreted to be due to a near axial symmetry crystal field. Luminescence from two of the states is directly observed as zero-phonon lines whereas only a phonon replica of the third one was detected. The excitation spectrum of the neutral isolated Se double donor was observed by photoconductivity measurements which establish that substitutional Se is present in detectable amounts in the samples even for the 9 min samples. It is speculated that the photoluminescence bands are related and/or are precursors to the previously reported bands that are observed after considerably longer diffusion times.