TIME-RESOLVED PHOTOLUMINESCENCE OF POROUS SILICON

The photoluminescence emitted by porous silicon under conditions of continuous (Ar+ laser) and pulsed (N2 laser) photoexcitation at temperatures 4.2-300 K have been studied. The spectrum of the photoluminescence generated by continuous excitation (''static'' spectrum) contained a wide structure-free band. The time-resolved spectra (time resolution 20 ns) differed fundamentally from the static spectra. Two luminescence bands were emitted by porous silicon. The short-wavelength band A1 with a maximum at 2.5 eV was observed in the nanosecond range of delay times (0-70 ns). The long-wavelength band A2 shifted with increasing delay time toward the red part of the spectrum and became dominant after > 100-ns delays. The observed transformation of the spectra with time was due to a strong dependence of the carrier lifetime on the diameter of a quantum wire, because porous silicon could be regarded as a set of such wires; it was also due to migration of excitations.