Photoluminescence from erbium incorporated in oxidized porous silicon

In the present work, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy were used to study oxidized porous silicon (OPS) doped with Er by electrochemical migration. Three types of OPS were investigated: (a) partially oxidized PS (POPS); (b) fully oxidized PS (FOPS); (c) oxidized PS co-doped with Fe (OPS:Fe). The OPS consists of oxide, Si nanoclusters and voids, and their composing fractions are dependent on the PS porosity and oxidation regime. The main result of this work is the assessment that the location of Er ions in composing fractions of OPS has a profound effect on the PL and PLE spectra. We show that for both POPS and FOPS, Er exhibits a broad 1530 nm PL spectrum similar to that observed in the Er-doped silica glasses. For POPS, the PLE spectrum of the 1530 nm Er PL band consists of a superposition of sharp peaks, which are attributed to the absorption transitions of Er ions incorporated into the oxide fraction, and a broad band, which is related to the absorption band of Si nanoclusters. For FOPS, the PLE spectrum consists just of sharp peaks. In contrast to POPS and FOPS, for OPS:Fe, Er PL spectrum consists of 21 highly resolved peaks. PLE spectrum of the strongest 1535 nm PL peak represents a wide band which is attributed to the absorption band of Fe:O nanoclusters formed inside OPS:Fe. Mechanism of excitation and luminescence of Er ions in OPS is presented.