EFFECT OF OXIDATION TREATMENTS ON PHOTOLUMINESCENCE EXCITATION OF POROUS SILICON

We have studied the effect of various controlled surface oxidation tre atments on photoluminescence excitation spectra of porous silicon for various omission energies. The UV excitation spectra of fresh samples were found to be peaked with a monotonic relation between peak excitat ion energy and emission energy, and to have an onset near 3.3 eV, the direct gap of Si. Aging (ambient oxidation) was found to unevenly affe ct the excitation spectra, resulting in an effective red shift of the peak center. On the other hand, anodic oxidation or oxidation by expos ure of the sample to copper ions in solution caused a blue shift of th e excitation spectra. These results are explained in terms of surface condition effects on nonradiative loss sites or on the interquantum do t barriers. (C) 1997 American Institute of Physics.