COMPARISON OF ANODICALLY ETCHED POROUS SILICON WITH SPARK-PROCESSED SILICON

Anodically etched porous Si (AEPS) and spark-processed silicon (sp-Si) show interesting differences in some of their luminescence-related properties. Among these differences are: (1) the photoluminescence (PL) spectra of sp-Si have maxima between 550 and 410 nm (depending on the processing conditions) when sp-Si is excited at 325 nm, whereas PL spectra of conventional (unannealed) AEPS generally peak between 640 and 730 nm (depending on the degree of porosity); (2) the PL intensity of sp-Si remains relatively stable under UV illumination, whereas the PL intensity of conventional AEPS decreases substantially under these conditions; (3) the PL intensities of sp-Si and AEPS, when excited at 325 nm in the lower W cm(-2) range, are initially comparable; (4) the pumping wavelength has a definite influence on the PL spectra of sp-Si (in contrast, the peak wavelength of conventional AEPS stays essentially constant under varying excitation wavelengths); (5) spark-processed Si displays a stable and visible cathodoluminescence (when exposed to electrons having an energy of about 0.8 keV) whereas conventional AEPS visibly cathodoluminesces under the same conditions for only a fraction of a second; and (6) The vibrational spectra for sp-Si as measured with Fourier transform infrared spectroscopy (FTIR) favour those modes which involve silicon-oxygen bonds. FTIR spectra of conventional AEPS additionally show some hydrogen-related vibrational modes.