Ultrasensitive Self-Powered UV Photodetector Based on a Ti/n-4H-SiC/n⁺⁺-4H-SiC Double Junction

Self-powered ultraviolet (UV) photodetectors (PDs), which directly convert UV photons into measurable electrical outputs, have broad application prospects in environmental monitoring, aerospace, and life sciences. In this work, we present an ultrasensitive energy converter PD based on a double junction (DJ) structure (Ti/n-4H-SiC Schottky junction and n-4H-SiC/n⁺⁺-4H-SiC homojunction) to overcome the technological obstacles of narrow-band-gap and higher leakage currents in silicon-based PDs. The working principle is based on the UV photogeneration of electron-hole pairs, splitting, and then transportation by the built-in potentials present at the DJ interfaces. Further, the increasing power intensities (from 2 to 10 mW/cm²) enhanced the photogenerated electron-hole pairs. The accumulation of photogenerated holes on the semiconductor side of the Schottky interface further reinforced the interfacial potential, promoting more efficient charge carrier separation and transport. Thus, a larger vertical photoresponsivity of 1.597 × 10^-2 A/W, a high specific detectivity of 6.90 × 10¹¹ Jones, and an external quantum efficiency of 6.61% with shorter response times (rise time/decay time of 96/96 ms) are achieved under 300 nm UV light irradiation at 10 mW/cm², surpassing most studies on 4H-SiC PDs. Benefiting from its simple architecture and superior photovoltaic performance, the current research demonstrates the potential of the DJ structure in micro/nano-electromechanical systems, optoelectronic sensors, and energy harvesters.