Optical properties of porous silicon layers processed with a HF : HCl : C2H5OH electrolyte

The properties of porous silicon samples prepared by adding hydrochloric ac id to the usual hydrofluoric-acid electrolyte have been studied. These samp les exhibit an intense photoluminescence that does not degrade over time an d is unaffected by exposure to intense laser illumination. The peak photolu minescence from these layers of porous silicon occurs at photon energies of 1.85 - 1.9 eV. The photoluminescence signal from samples prepared in the s tandard way under the same initial conditions but without HCl in the compos ition of the electrolyte is two orders of magnitude less intense. Studies o f the degradation of these porous silicon samples with time and exposure to various power levels of laser illumination revealed that the samples with the maximum content of HCl in the electrolyte composition emitted photolumi nescence that was unaffected by laser illumination. In this work, the infra red spectra of the samples was measured in order to monitor the chemical st ate of their surfaces. It was found that the abrupt 100-fold increase in th e intensity of the photoluminescence signal from samples made according to the method proposed here is associated both with distinctive features of th e structure of porous silicon layers and with the presence of a thin crysta lline layer of SiO2 on the surface of nanocrystallites. (C) 1999 American I nstitute of Physics. [S1063-7826(99)00902-3].