Demonstration of AlGaN solar-blind ultraviolet photoconductor with an ultra-fast nanosecond transient response

Conventional AlGaN solar-blind ultraviolet (UV) photoconductors based on Si- or Ge-doped conduction channels are plagued by the impurity-related persistent photoconductivity (PPC) effect featuring high leakage current, long response time, severe sub-bandgap photoresponse, and narrow linear dynamic range (LDR). In this work, we propose what we believe to be a novel photoconductor architecture based on the Al_0.6Ga_0.4N/Al_0.45Ga_0.55N heterojunction structure. Due to the polarization-induced two-dimensional electron gas (2DEG) beneath the Al_0.6Ga_0.4N barrier layer, low-resistance Ohmic contacts can be obtained to ensure the photoresponse. Owing to the employment of unintentionally doped Al_0.45Ga_0.55N channel layer as the photosensitive area, the PPC effect is effectively suppressed. The proposed device exhibits a high photoconductive gain above 400, an extremely low leakage current on the order of fA, a large photo-to-dark-current ratio (PDCR) over 10⁷, a superior solar-blind rejection ratio (SBRR) over 10⁴, a high specific detectivity above 1 × 10¹³ Jones, and a wide LDR of 80 dB. Most impressively, an ultra-fast nanosecond response time (12 ns/236 ns) is achieved for the first time, which overturns the long-held perception that photoconductive detectors are inherently slow. Overall, this work presents a simple yet effective approach toward high-speed, high-sensitivity, and low-noise solar-blind UV detection.