Time-resolved photoluminescence spectroscopy of Er-implanted porous silicon

We have investigated the time evolution of the 1.54 μm Er³⁺ photoluminescence (PL) intensity of Er-implanted porous silicon in the temperature range from 15 to 375 K. Er was implanted into porous silicon with a dose of 1 x 10¹⁵ Er/cm² at 380 keV and annealed at 605°C for 30 min. Upon optical excitation at 488 nm, erbium ions are excited by photogenerated carriers and an intense 1.54 μm PL is observed at room temperature. We have compared the time evolution of the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ to a double-exponential decay. The analysis suggests the existence of two classes of Er sites in porous silicon. This is supported by a study of the Er³⁺ PL decay time as a function of excitation pulse width. The characteristic Er³⁺ lifetimes in the two sites are 145 μs and 1.37 ms, respectively. In the temperature range from 15 to 150 K, the back transfer of energy from the excited erbium level ⁴I_13/2 to the host plays the dominant role in the thermal quenching of the Er³⁺ luminescence. At temperatures above 150 K, the reduction in Er³⁺ PL can mainly be ascribed to thermalization of bound electrons to the conduction band. We have compared the observed Er³⁺ PL intensity with the result from a theoretical model and a good agreement is obtained.