Versatile approaches to tune a nanocolumnar structure for optimized electrical properties of In₂O₃ based gas sensor

In this study, we demonstrate tuning of electrical properties and sensing responses of In₂O₃ nanocolumnar structure via varying glancing angle (GLAD) deposition conditions by e-beam evaporator. The varied deposition conditions include glancing angle, vacuum level and deposition rate. The electrical property of In₂O₃ nanostructured thin films, demonstrated by the base resistance, change up to 3 orders of magnitude from 110 Ω to 103104 Ω depending on the porosity of nanocolumnar structure and oxygen vacancy concentration. This variation in electrical property transfers to the tuning of gas sensing response, and we achieve tuning the same material (In₂O₃) based gas sensors to better perform for specific type of gases (either oxidizing or reducing). The highest responses achieved in this work reached up to 176 for oxidizing gases (5 ppm NO₂, R_gas/R_air) and 929 for reducing gases (50 ppm C₂H₅OH, R_air/R_gas). Therefore, we demonstrate that gas sensors can be optimized for specific type of target gases with the same material, via simple control of deposition conditions. Along with the high reproduciblility and sensitivity, this puts the nanocolumnar thin film based gas sensors by GLAD with huge potential for further miniaturization and mass production, suitable for the upcoming IoT era.