Two types of carbon nanotubes [single walled nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs)] are deposited on porous silicon by the drop casting technique. Upon exposure to test gas mixing ratio 3% NO 2 , the sensitivity response results show that the SWCNTs' sensitivity reaches to 79.8%, where MWCNTs' is 59.6%. The study shows that sensitivity response of the films increases with an increase in the operating temperature up to 200• C and 150℃ for MWCNTs and SWCNTs. The response and recovery time is about 19 s and 54 s at 200℃ for MWCNTs, respectively, and 20 s and 56 s at 150℃ for SWCNTs.

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CdS nanoparticles have been prepared by a chemical method and deposited as a thin film on both P-type silicon and porous silicon (PS) substrates by spin coating technique as a photoconductive detector. The Hall measurements show that the nanoparticles are n-type with carrier concentration of about (− 5.45 × 10 10 cm −3). The response time of the fabricated detectors on Si, PS and (CdS + TPD/PS) substrates was measured (by illuminating the sample with Halogen lamp 250 W) and its values are 5.2 ms, 2.1 ms and 1.3 ms, respectively. The specific detectivity and photoresponsivity of the fabricated detector on PS are found to be (9.9 × 10 12 Watt −1 Hz 1/2 cm −1 and 0.043 A/W). The surface functionalization of the CdS nanoparticles film deposited on porous silicon (PS) substrate by triphenyldiamine (TPD) has highly improved the photoresponsivity and response time of the detector to 0.059 A/W and 1.3 ms.

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