An Efficient Room Temperature Ethanol Sensor Device Based on p-n Homojunction of TiO2 Nanostructures

In this paper, an efficient room temperature ethanol sensor device based on p-n homojunction of p-TiO
₂
nanoparticles (NPs) and n-TiO
₂
nanotubes (NTs) is reported. p-TiO
₂
NPs were prepared by low-temperature sol-gel method and coated on n-TiO
₂
NTs (NPs) grown by electrochemical anodization. Field emission scanning electron microscopy and X-ray diffraction authenticated the formation of stable homojunction between p-type anatase TiO
₂
NPs and n-type anatase TiO
₂
NTs. Current-voltage characteristics of the device, in the lower voltage range (0-1.26 V) for 30 °C, followed nonlinear characteristics (Schottky). With increase in voltages (>1.26 V) and temperature (40 °C-100 °C) such nonlinear behavior moves toward more linear ones. The gas sensing performance of the homojunction device was studied at room temperature with alcohols as the test species. The device offered the maximum response magnitude of ~57% (toward ethanol) at 100 ppm with appreciably fast response time and recovery time of ~30 and ~16 s, respectively. Dramatic increase in the effective depletion region area distributed throughout the nanotubular voids and the associated localized electric filed originated from the electrostatic charge separation therein (which helps in easy dissociation of target species) is possibly responsible for such efficient room temperature sensing performance.