Large enhancement of ultra-violet photoresponse of silicon-nanoparticle-embedded porous silicon thin films by rapid-thermal-oxidation treatment

•Si-nanoparticle embedded porous silicon thin films were prepared on Si substrates.•The prepared films got greatly enhanced UV photoresponses after RTO treatments.•Photodiodes based on the developed films had large UV photo-to-dark current ratios.•This paper presented a novel approach to fabricating Si-based UV photodetectors.

The ultra-violet (UV) photoresponses of silicon-nanoparticle-embedded porous silicon thin films that were prepared from electrochemical-etching silicon substrates in an anodization process had been greatly enhanced by rapid-thermal-oxidation (RTO) treatment. Experimental analysis demonstrated that the optical bandgap energy of the formed nanoporous silicon (NPS) films increased from 1.6 eV to 3.5 eV after the RTO process. It was supposed that this bandgap-widening effect resulted from the size shrinking of Si-nanocrystals embedded in the oxidized NPS films and led to the large increase in UV responses. With RTO treatment of 90 s, the oxidized NPS films exhibited high UV photoresponses for incident light of wavelength between 300 nm and 400 nm, with peak photoresponsivity of 78 mA/W at 375 nm. In addition, under illumination of 350-nm UV light, the photodiode based on these RTO-treated NPS films got a 370-time larger photo-to-dark current ratio (PTDR) than that of one fabricated without RTO treatment. Therefore, oxidized NPS materials prepared by RTO treatment after the electrochemical-etching of Si wafers have high potential for development of Si-based UV photodetectors.

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