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Raman-scattering in electroluminescent porous silicon

: Kozlowski, F.; Steiner, P.; Lang, W.

Kiefer, W.; Cardona, M.; Schaack, G.; Schneider, F.W.; Schrötter, H.W.:
13th International Conference on Raman Spectroscopy '92. Proceedings
Chichester: Wiley and Sons, 1992
International Conference on Raman Spectroscopy <13, 1992, Würzburg>
Fraunhofer IFT; 2000 dem IZM eingegliedert
Elektrolumineszenz; poröses Silizium; Ramanspektroskopie; Strukturuntersuchung

We used Raman-scattering to investigate our electroluminescent porous silicon (LEPOS) made from n and pplus silicon substrates. To form the porous silicon from the n substrates, we used a DI- water/alcohol/HF-mixture containing 25 wt. percent HF. During the fabrication additionally illumination was applied. A current density 60 mA/qcm was used. The pplus porous silicon sample was produced without illumination in a 40 wt. percent HF solution and with a current density of 120 mA/qcm. The detailed fabrication process is described elsewhere . Samples made from p substrates showed no electroluminescence (EL) but only photoluminescence (PL), though other groups of researchers reported to have fabricated EL p-porous silicon . For the investigated samples we noticed, that those with EL-properties showed a Raman- spectrum having a relatively sharp (ca. 5-10 cmhigh-1) peak at about 519 cmhigh-1 and a shoulder at about 510 cmhigh-1 (type I-spectra) . Our non-EL p-samples have their peak at about 512 cmhigh-1 and a FWHM of 37plusminus7 cmhigh-1 (type II-spectra) . Tensile stress is known to be present in the porous silicon samples. Due to this stress, the peak of the Raman- signal can be shifted to lower energies up to 2 cmhigh-1.