Pd sensitized porous silicon hydrogen sensor—Influence of ZnO thin film

The Pd sensitized porous silicon (PS) hydrogen sensor with a thin zinc oxide (ZnO) over layer demonstrated the improved gas response behaviour at the higher temperature. Porous silicon was produced by the electrochemical anodization of the p-type monocrystalline silicon substrate of the resistivity, 2–5 Ω cm and (1 0 0) orientation, using a mixture of HF and ethanol as the electrolyte. The ZnO thin film was coated on the unmodified and on the Pd modified PS surfaces by the sol–gel dip coating method. The catalytic electrode to ZnO was the Pd–Ag (26 wt%) alloy and the contact electrode to the p-silicon substrate was Al. The effect of the Pd modified ZnO on the hydrogen sensing was also studied. The detail gas sensor study with the Pd–Ag/Pd:ZnO/Pd:PS/Si/Al structure indicates that the Pd sensitized ZnO on the Pd modified PS exhibits the minimum fluctuations in the current and the consistent hydrogen sensing performance including an improved gas response (86%), the response time (28 s) and the long-term stability. However, the long recovery time (∼290 s) is due to the slower desorption kinetics after the hydrogen cut off, for using nitrogen carrier gas instead of air that helps in avoiding the cross-sensitivity from the oxygen in air.