Gallium oxide (Ga ₂ O ₃ ) is an emerging semiconductor for advanced optoelectronic applications owing to its suitable bandgap and advantageous electronic characteristics. While amorphous Ga ₂ O ₃ is highly desired for low-cost and large-scale device application, it suffers from high dark current and slow response speed for practical ultraviolet photodetection. Here we integrate a polar aluminum nitride (AlN) template with amorphous Ga ₂ O ₃ to fabricate a fast-response metal semiconductor metal (MSM) photodetector. It is revealed that the carrier transport and device performance strongly depend on the polarization direction of the AlN template. With a downward polarization from an Al-polar AlN layer, the Ga ₂ O ₃ photodetector achieves an optimized performance with a lower dark current of 0.015 nA, a higher photo-to-dark current ratio of 10 ⁴ , a faster response speed of 31 ms and a recovery time of 22 ms. This study demonstrates an effective route of engineering carrier transport via the external spontaneous polarization for fabricating high-performance solar-blind photodetectors.

We report a GaN-based self-powered metal–semiconductor–metal (MSM)-type ultraviolet (UV) photodetector (PD) by employing a “lateral polarity structure (LPS)” grown on the sapphire substrate. An in-plane internal electric field and different Schottky barrier heights at a metal/semiconductor interface lead to efficient carrier separation and self-powered UV detection. A dark current of 6.8 n A / c m 2 and detectivity of 1.0 × 10 12 Jones were obtained without applied bias. A high photo-to-dark current ratio of 1.2 × 10 4 and peak responsivity of 933.7 mA/W were achieved for the lateral polarity structure-photodetector (LPS-PD) under − 10 V . The enhanced performance of the LPS-PD was ascribed to the polarization-induced carrier separation as demonstrated by the lateral band diagram.