Erbium in oxygen-doped silicon: optical excitation

The photoluminescence of erbium-doped semi-insulating polycrystalline and amorphous silicon containing 30 at. % oxygen is studied. The films were deposited on single-crystal Si substrates by chemical vapor deposition, implanted with 500 keV Er to fluences ranging from 0.05 to 6 x 10¹⁵ ions/cm², and annealed at 300-1000 ^oC. Upon optical pumping near 500 nm, the samples show room-temperature luminescence around 1.54 µm due to intra-4ƒ transitions in Er³⁺, excited by photogenerated carriers. The strongest luminescence is obtained after 400 ^oC annealing. Two classes of Er³⁺ can be distinguished, characterized by luminescence lifetimes of 170 and 800 µs. The classes are attributed to Er³⁺ in Si-rich and in O-rich environments. Photoluminescence excitation spectroscopy on a sample with 1 X 10¹⁵ Er/cm² shows that ~2% of the implanted Er is optically active. No quenching of the Er luminescence efficiency is observed between 77 K and room temperature in this Si-based semiconductor. The internal quantum efficiency for the excitation of Er³⁺ via photogenerated carriers is 10^-3 at room temperature. A model is presented which explains the luminescence data in terms of trapping of electrical carriers at localized Er-related defects, and subsequent energy transfer to Er³⁺ ions, which can then decay by emission of 1.5 µm photons.