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.© 1995 American Institute of Physics.