Microscopic model for nonexcitonic mechanism of 1.5-μm photoluminescence of the Er³⁺ ion in crystalline Si

Excitation mechanisms of Er³⁺ ion in crystalline silicon, responsible for the photoluminescence at ? ˜ 1.54 µm, are reexamined in view of the new information revealed for this system by two-color spectroscopy in the visible and the midinfrared. We argue that the appearance of the midinfrared induced emission from the ⁴I_13/2 excited state of Er³⁺ and the recently identified afterglow effect represent characteristic fingerprints of a specific and so far unrecognized excitation path, different from the usually considered exciton-mediated energy transfer. We propose a microscopic model of this mechanism, where excitation of Er³⁺ is accomplished in two distinct steps: electron localization at an Er-related donor level and its subsequent recombination with a hole. These two stages can be separated in time, leading to a situation when the appearance of Er photoluminescence is controlled by availability of one carrier type only. We propose a set of rate equations to describe this process and show that the experimental data are well accounted for. Further, we consider potential of the nonexcitonic mechanism for realization of efficient temperature-stable emission from Er-doped crystalline silicon.