Silicon carbide photodetector has enhanced response in the near-UV

Feb. 18, 2020
By thickening the i (intrinsic) semiconductor layer, the photoresponse of a silicon carbide (SiC) Schottky diode was boosted in the 270–350 nm region.

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 270350 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.

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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