Time-resolved photoluminescence spectroscopy of Er-implanted porous silicon

We have investigated the time evolution of the 1.54 mu m 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 10(15) Er/cm(2) at 380 keV and annealed at 605 degrees C for 30 min. Upon optical excitation at 488 nm, erbium ions are excited by photogenerated carriers and an intense 1.54 mu m PL is observed at room temperature. We have compared the time evolution of the I-4(13/2) --> I-4(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 mu s and 1.37 ms, respectively. In the temperature range from 15 to 150 K, the back transfer of energy from the excited erbium level I-4(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.