A Junction Photoconductive Semiconductor Switch (J-PCSS) in AlN With Sub-Band Gap Responsivity and Accelerated Turn-Off Speed

A photoconductive semiconductor switch (PCSS) made from ultra-wide band gap AlGaN is promising in high power applications. However, stimulating intrinsic photoconductivity requires deep ultraviolet (UV) light, which compromises system cost and reliability. Here we report a PCSS that uses extrinsic photoconductive response to sub-bandgap visible light in Ge-doped AlN. With blue LED (455 nm center wavelength) illumination, and irradiance as low as 1 mW/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, the PCSS achieves photocurrent density of 0.9 uA/mm, 5 orders-of-magnitude on/off ratio, and optical responsivity of 18 A/W. PCSS devices often suffer from slow turn-off due to persistent photoconductivity (PPC). We demonstrate suppression of PPC using a Schottky junction to control the Fermi energy within the AlN channel. Using this device geometry, that we call a junction-PCSS (J-PCSS), we achieve substantial speed-up of device turn-off. These results pave the way for fast switching and high optical gain AlGaN power devices triggered with visible illumination.