Low-Level UV Detection Using Channel-Width Optimized TiO₂ Phototransistor

We report on the fabrication and UV photoresponse characteristics of TiO 2 -based phototransistors (TiO 2 –PTs) incorporating a TiO 2 /SiN active layer grown on Si substrates via electron beam evaporation. Devices with fixed channel length (∼2.5 μm) and varying channel widths (6.0, 7.5, and 9.0 μm) were fabricated to examine geometric effects on optoelectronic behavior. All PTs exhibit well-defined I – V characteristics and strong UV sensitivity under 18 μW, 385 nm illumination. The widest channel device (9.0 μm) demonstrated a peak responsivity of 10.5 A/W and a detectivity of 6.6 × 10 10 Jones at V GS = 5 V, outperforming narrower geometries in terms of carrier collection and photocurrent generation. Narrower channels demonstrate sharper switching (SS ∼ 10 V/dec) but reduced photocurrent gain due to limited absorption volume. These results highlight the crucial role of channel-width engineering in modulating responsivity, switching efficiency, and signal-to-noise characteristics. This study provides a scalable pathway for optimizing TiO 2 -based FET photodetectors for high-sensitivity UV imaging and environmental sensing applications.