Fabrication of a Red-Sensitive Heterojunction Photodetector by Using a Narrowband Organic Dye

Narrowband photodetectors in the visible region are in demand for different applications, such as image sensors. In this work, a narrowband photodetector is fabricated by coating a red-sensitive organic dye (squaraine, SQ2) on top of a metal oxide heterojunction consisting of zinc oxide (ZnO) and titanium oxide (TiO₂). The formation of the heterojunction helps in effective charge separation at the interface, which in turn improves the overall sensitivity of the photodetector. Electrical characterization studied under light illumination and external quantum efficiency measurements reveal that the photodetector has selective sensitivity in the red region with a peak position at 650 nm and full width at half-maximum of 116 nm. The device shows a significantly low dark current (1.72 nA under 10 V bias) with a detectivity of 2.57 × 10¹⁰ Jones (under 1 V external bias). These characteristics suggest that squarylium dye-based red-light photodetectors are suitable for visible light communication and other narrowband photoelectric applications such as image sensors.