Photoluminescence and Raman study of porous silicon synthesized by visibleand infrared laser etching

Visible and infrared lasers have been used to photochemically fabricate pho toluminescent porous silicon thin films on n-type silicon substrates. Photo luminescence measurements on porous silicon exhibit a two-peak structure fo r argon-ion laser etching. It is found that the intensity ratio for the two photoluminescence peaks at 1.91 and 2.02 eV is reversed on changing the ex citation photon energy from 2.41 to 2.71 eV. Etching with a Nd:YAG laser, o n the other hand, yields a single PL band. Raman measurements from the two porous silicon samples also show different behavior, both in the location o f the peaks, as well as in the asymmetry of Raman lines in first-order spec tra. These results are analyzed using a quantum confinement model for photo luminescence and Raman spectra. Mean nanocrystallite size and the size dist ribution parameters are studied here as a function of excitation energy in the photoluminescence and Raman spectra. (C) 2001 Elsevier Science B.V. All rights reserved.