High efficiency 4H-SiC Schottky UV-photodiodes using self-aligned semitransparent contacts

In this work, we report on 4H-SiC vertical Schottky UV-photodiodes, with a novel "semitransparent" electrode, using self-aligned Ni2Si interdigit contacts, that allow operation in the pinch-off regime of the directly exposed optically active area. This improves short wavelength detector sensitivity with respect to conventional semitransparent Schottky UV detectors which use thin metal films. Computer simulations of the electric field distribution were used to optimise the device's front electrode Geometry, maximising the pinch-off surface effect. The detector dark current was about 200 pA at -50 V thanks to the high Schottky barrier of the Ni2Si on the 4H-SiC (1.66 eV). Under illumination with radiation at 254 nm, an increase of the current of more than two orders of magnitude is observed, resulting in 78% internal quantum efficiency. The vertical photodiodes showed an ultraviolet-visible rejection ratio of about 104 and a current responsivity factor of 1.8 higher than a conventional planar metal-semiconductor-metal interdigit structure.