Transport Pathway Engineering in a Three-Terminal Diamond Schottky Photodiode for High-Temperature Dual-Mode Solar-Blind Ultraviolet Detection

Diamond is promising for solar-blind ultraviolet (SBUV) photodetection in high-temperature extreme environments. However, stable self-powered operation and high-gain response are difficult to reconcile in diamond photodetectors. Photovoltaic diamond photodiodes offer stable zero-bias operation at the expense of limited responsivity, whereas photoconductive-type devices provide gain but often compromise thermal robustness. Here, we introduce transport-pathway engineering in a three-terminal diamond Schottky photodiode to realize dual-mode high-temperature SBUV detection. The device consists of a common Pt/O-terminated diamond Schottky terminal on a single-crystal boron-doped diamond epitaxial platform, together with a backside ohmic terminal and a coplanar ohmic terminal that share the same diamond drift layer. By selecting the carrier-collection terminal, this three-terminal architecture defines either one-dimensional vertical transport (VT) or mixed vertical–lateral transport (VLT) within a unified diamond Schottky photodiode. From 300 to 580 K, the VT pathway supports low dark current, stable self-powered photovoltaic operation with a root-mean-square current fluctuation of 0.81 fA, whereas the VLT pathway enables high-gain biased detection at elevated temperature. Under 215 nm illumination at 580 K, the high-gain detection mode achieves a responsivity of 919.2 A·W–1 at 10 V and a specific detectivity of 7.72 × 1013 Jones under the shot-noise-limited approximation. These results demonstrate that transport-pathway engineering provides a route to complementary self-powered photovoltaic and high-gain biased operating modes in thermally robust diamond Schottky photodiodes for high-temperature optoelectronics.