A Unique VO2 Heterojunction-Based Ultrafast Photodetector Configuration for Exceptional Quantum Efficiency and Superior Responsivity

Metal–semiconductor–metal (MSM) photodetectors (PD) are highly versatile and beneficial in a vast array of optical and optoelectronic systems. Although vanadium dioxide (VO₂) has a high broadband absorbance, its distinctive electrical and structural features have mostly been utilized for near-infrared (NIR) photodetection. Here, we propose a unique design for a PD using a heterojunction made of VO₂/oxygenated-Ti (Ti–O) sandwiched between two Au electrodes. The VO₂ film acts as a photon accumulator in this arrangement, and the band bending at the VO₂/Ti–O interface helps to separate charges to reduce carrier recombination and inject electrons into the more conductive Ti–O layer. The design completely eliminated all size restrictions of the active layer, regardless of its electrical conductivity, and demonstrated superiority in almost all performance metrics. A remarkable photocurrent density of around 57 μA/cm² and a rapid response time of 1–2 ms in the presence of visible light was seen at a low bias voltage of 100 mV. The highest detectivity and photocurrent density obtained in our experimental range were 3.2 × 10¹⁰ Jones, and 465 μA/cm², respectively, using an 800 mV bias voltage and 590 nm light (power density: 76 μW/cm²). For VO₂(M)-based MSM type devices, the proposed PD design exhibited the highest responsivity of approximately 2.54 A/W and an exceptional external quantum efficiency (EQE) of around 534%.