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To improve the stability of porous Si (PS) prepared by electrochemical etching, we make use of rapid-thermal oxidation (RTO). During RTO processing, the hydride coverage of the internal surfaces of the pores is replaced by a high-quality oxide while retaining nm-sized Si grains. With increasing process temperature Tox the luminescence is first quenched. It is recovered with comparable intensity for Tox≥700 °C.

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The visible luminescence of porous Si is known to contain at least two spectrally distinct emission bands with widely different response times. The orange-red luminescence component (1.5–1.9 eV) decays in times being of the order of 10 μs at room temperature. The blue-green band (2.3–2.6 eV) is very much faster with response time in the 10-ns range. It is shown that with increasing degree of oxidation the fraction of the fast luminescence intensity rises from ∼1% of the total in the as-prepared porous Si to become the dominant spectral component in strongly oxidized material. For the rapid-thermal-oxidized material excited with 337-nm radiation, the intensity of the fast luminescence is comparable to that in the as-prepared state.