Study of porous silicon surface properties

Kok Wai CHEAH*, T. Y. Leung, Mau Hing CHAN, Shu Kong SO

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review


Porous silicon is a material with a coral-like structure which has a fractal surface. To study these aspects of porous silicon and its relationship with the luminescence property, we have used atomic force microscopy (AFM). Samples were prepared using either pure HF or HF diluted with ethanol. From the results of AFM, distinct structural difference was observed from samples prepared by these two etchants. If we relate the structures to their respective photoluminescence spectra, it appears that finer structure produced shorter wavelength peak photoluminescence. However, the columns of the samples were too large for one to attribute the luminescence to quantum confinement only. Hence, an alternative model may be required to explain the luminescence mechanism. We have also observed that the composition of the etchant can also affect the evolution of the fractal dimension with respect to etching time. Probing of the surfcace electron states was performed using photothermal deflection spectroscopy (PDS). In order to ensure that only porous silicon layer was probed, free-standing films of various porosity were produced for the PDS measurement. The probe energy range was from 0.56 eV to 2.5 eV so that both the bulk states and the surface states were probed. The results showed that there is a clear blueshift of the energy band gap with respect to porosity, and the absorption coefficient decreases with porosity increase at a fixed photon energy. Overtones of hydrides and fluorides of silicon were also observed.

Original languageEnglish
Pages (from-to)1235-1239
Number of pages5
JournalSurface Review and Letters
Issue number2
Publication statusPublished - Apr 1996

Scopus Subject Areas

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry


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