Exploring the Potentiality of ZnO-BJT for Efficient Detection of Low Concentration Alcohols Through Innovative Utilization of Transistor Properties

A novel alcohol sensor device based on ZnO bipolar junction transistor (BJT) is reported, where the fields related to two junctions and the inherent current gain (
$\beta \sim 24$
) properties of the device were utilized innovatively to improve the sensing performance. Two pivotal material features essential for gas sensing, e.g., nanostructures and non-stoichiometry of the constituent layers, were authenticated through Field-Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray (EDAX), and Atomic Force Microscopy (AFM). The sensing performance of the device was evaluated from the changes in the collector current (
${I}_{C}$
) in the active region [in common emitter (CE) mode at room temperature, 27 °C] with exposure to methanol vapor (as a test case) considering the device performance in air as the reference. Remarkable improvement in the lowest detection limit (125 ppb) was achieved with fairly good sensitivity over the entire dynamic range (~25% at 125 ppb to ~86% at 200 ppm). The underlying mechanism for such increased sensitivity, even at low concentration regime, was explained in the light of the corresponding energy band diagram of the device as a function of the bias condition and gaseous ambient. Double-junctions-related electric field-induced dissociation of target species resulted in efficient low-concentration detection ability.