Time-delayed luminescence from oxidized porous silicon after ultraviolet excitation

Oxidized porous silicon is known to luminesce efficiently and with a ns-fast response in the green-blue region of the spectrum (2.3–2.7 eV) at room temperature. For microporous Si processed by rapid thermal oxidation at 1100–1200 °C in a dry oxygen ambient, we observe that the blue light has a time-delayed component that indicates carrier trapping. In addition to the well-established ultrafast light (∼1 ns) a signal with a time delay of order 1 s is present under UV photoexcitation. The time-delayed blue light exists at low temperature and has an excitation onset edge at 4.3±0.1 eV, an energy that is usually associated with a band discontinuity at the Si–SiO2 interface.