Exploring ZnO-Based pn Homojunction for Gas Sensing Applications: Fabrication and Performance Evaluation

In this study, we have developed engineered ZnO-based p-n junction NO₂ gas sensors with exceptional sensitivity and selectivity. Initially, undoped ZnO and Na-doped ZnO films were synthesized using RF sputtering and the sol-gel technique, respectively. A comprehensive investigation of the material properties, including structural, elemental composition, morphological characteristics, and electrical behavior, was conducted. Hall measurement studies confirmed that undoped ZnO functions as an n-type semiconductor with a resistivity of 6.76 × 10 ³Ω/cm., while Na-doped ZnO exhibits p-type semiconductor characteristics with a resistivity of 1.77 × 10 ³Ω/cm. I-V measurements at room temperature demonstrated a clear rectifying behavior of the ZnO-based p-n homojunction, which was further validated by simulation results obtained using Silvaco TCAD, showing excellent agreement with the experimental data. The NO₂ gas sensing performance of the fabricated ZnO homojunction was evaluated, revealing superior sensitivity at an optimal operating temperature of 240 °C. The sensor achieved a remarkable response of 1656%, with rapid response and recovery times of 20 s and 93 s, respectively, for a test gas concentration of 45 ppm. The ZnO homojunction demonstrated detection capability at 1 ppm and high NO₂ selectivity characteristics in the presence of other gases like NO, NH₃, and acetone. The long-term stability of the fabricated homojunction sensor underscores its reliability and efficiency as a gas-sensing device.