Back-Gate GaN Nanowire-Based FET Device for Enhancing Gas Selectivity at Room Temperature

In this work, a TiO₂-coated GaN nanowire-based back-gate field-effect transistor (FET) device was designed and implemented to address the well-known cross-sensitive nature of metal oxides. Even though a two-terminal TiO₂/GaN chemiresistor is highly sensitive to NO₂, it suffers from lack of selectivity toward NO₂ and SO₂. Here, a Si back gate with C-AlGaN as the gate dielectric was demonstrated as a tunable parameter, which enhances discrimination of these cross-sensitive gases at room temperature (20 °C). Compared to no bias, a back-gate bias resulted in a significant 60% increase in NO₂ response, whereas the increase was an insignificant 10% in SO₂ response. The differential change in gas response was explained with the help of a band diagram, derived from the energetics of molecular models based on density functional theory (DFT). The device geometries in this work are not optimized and are intended only for proving the concept.