Macroporous Silicon (MPS) with Embedded NiO Thin Film for CO2 Gas Sensing

In this work, an Al/NiO/MPS/n-Si structure has been used to detect CO 2 gas at different concentrations. NiO thin films were deposited by sol–gel dip-coating method onto macroporous silicon (MPS) and glass substrates. The structural and optical properties of the NiO films have been also studied. The XRD characterization shows that the NiO films are polycrystalline with a (200) preferential orientation; the optical band gap of the NiO film determined by spectrophotometry using the Tauc relation is found 3.9 eV. The electrical characteristics of the Al/NiO/MPS/n-Si structure such as current–voltage ( I – V ), sensitivity–voltage ( S – V ) and current–time ( I – t ) measurements have been carried out at room temperature in the presence of CO 2 gas. The results show that the electrical characteristics of the sensor are modified in the contact of CO 2 gas. The developed sensor exhibited high sensitivity and fast responses. Finally, the mechanisms of CO 2 gas and NH 3 vapour sensing based on PN heterojunction (NiO/MPS) have been proposed.