Laser Heating in Porous Silicon Studied by Micro-Raman Spectroscopy

Abstract

We have measured the temperature rise in nanoporous silicon under strong illumination. A green laser beam was focused with a microscope objective on porous silicon films with porosities between 55% and 80%. The Raman spectrum was measured for power densities between 0.8 and 65 kW/cm 2 . We obtained the temperature of the illuminated area from the shift of the phonon frequency when phonon confinement effects are removed. The temperature depends linearly on power density. For a given power density, the temperature increases with porosity for porosities below 60% as the thermal conductivity decreases. Beyond that point, the temperature decreases because the reduction of light absorption dominates. The maximum temperature reached was 400 C for a 60% porosity sample and for a power density of 65 kW/cm 2 .

Photoluminescence of oxidized porous silicon under UV-light illumination

“…Therefore, after the illumination, the blue emission of the oxidized N-type PS degraded slightly. In addition, there are several papers to discuss the thermal effect of laser radiation on the PL spectra of PS [21,22]. In these papers, the results show that, for small power densities and for meso porous and macro porous silicon, the thermal effect that was caused by laser irradiation is small.…”

Mechanical stress relief in porous silicon free standing membranes

“…The detector is an air cooled CCD (1024 x 256 pixels). The laser power was attenuated, during the spectra acquisition, down to about 0.7 mW in order to minimize the thermal effects (power density was about 10 4 W/cm 2 ), which is a conservative value to avoid thermal effects as demonstrated by literature [18,19]. No polarizers have been used and the measurements can be considered as non-polarized, as the informations on the Silicon crystalline direction after detachment of the PSi membrane are lost.…”

Laser-Induced Reversible and Irreversible Changes in Silicon Nanostructures: One- and Multi-Phonon Raman Scattering Study

“…The Journal of Physical Chemistry C ARTICLE elucidating correlations between laser-induced heat, chemical alterations, and potential errors resulting from the reversible Raman line shifts. 20,34,36,37 Also, to the best of our knowledge, there is no evidence of a systematic thermal treatment study to confirm the heat-related observations from laser-induced Raman line shift/broadening. Finally, the designation of the multiphonon scattering bands located at frequencies between 600 and 900 cm À1 and above 1000 cm À1 of the Raman spectra of silicon nanostructures remains controversial, 10,15,38 with disagreement as to whether these bands result from surface oxide or hydride bonds.…”

“…The effect of temperature increase on the Raman spectra of c-Si and different types of silicon nanostructure has been extensively studied. ,− Because of diversities in silicon nanostructures and difficulties in assigning an exact safe value for laser irradiance, controversies in reported laser powers used to acquire Raman spectra exist in the literature. ,− ,, Several works have investigated the effects of different laser wavelengths and powers on the Raman spectra of nanostructured silicon. ,, However, most of them have focused on temperature estimations rather than elucidating correlations between laser-induced heat, chemical alterations, and potential errors resulting from the reversible Raman line shifts. ,,, Also, to the best of our knowledge, there is no evidence of a systematic thermal treatment study to confirm the heat-related observations from laser-induced Raman line shift/broadening.…”