Photodetectors based on silicon carbide (SiC) perform well in the ultraviolet (UV) at wavelengths shorter than 260 nm and have low response in visible wavelengths, resulting in desired solar-blind or visible-blind performance. However, due to the high 3.26 eV indirect bandgap of SiC, absorption of near-UV light of wavelengths from 260 to 380 nm, and thus detection efficiency, is poor. Researchers at The University of Virginia (Charlottesville, VA) and the U.S. Army Research Laboratory (ARL; Adelphi, MD) have now created a SiC Schottky photodiodes with a thick i (intrinsic) region that has its absorption peak shifted to longer UV wavelengths, resulting in good performance in the 270–350 nm region.
Before fabricating the devices, which began as 1 × 1 cm squares diced from a double-sided polished SiC waver etched to remove surface oxide, the squares were controllably re-oxidized by heating them in pure oxygen to about 1300°C for 12 to 24 hours—this helped to increase the carrier lifetime of the bulk material. Devices with 20 and 50 µm i layers were fabricated. External quantum-efficiency measurements of the completed photodiodes were done using a laser-driven light source whose output was coupled into a monochromator and then into a 300-µm-diameter, low-UV-loss optical fiber and through two microscope objectives that focus the light to a spot on the photodiode. The 20 µm i layer resulted in a 37% quantum efficiency at 330 nm, while the 50 µm i layer produced a 40% quantum efficiency at 350 nm, both showing that a thick i layer was the path to near-UV photoresponse. Reference: Y. Shen et al., Appl. Phys. Lett. (2019); https://doi.org/10.1063/1.5129375.
