Attachable freezing-delayed surfaces for ultraviolet sensing using GaN photodetector at low temperature in air

The enhanced optical sensitivity of gallium nitride (GaN) ultraviolet (UV) photodetectors is demonstrated using attachable and hydrophobic freezing-delayed surfaces. The GaN surface attached to microfabricated surfaces with an array of pyramid structures reduced the surface reflectance compared with that of bare GaN surface (∼43.3% decrease at 365 nm wavelength). In addition, as the operation temperature decreased, the hydrophobic pyramid microstructures prevented rapid frost formation by generating dispersed and small-sized frosts (ice crystals). Consequently, the photodetectors fabricated using hydrophobic surfaces with pyramid microstructures showed higher sensitivity (∼48.5% increase in the temperature range of −14 °C to 0 °C) compared to the photodetectors on bare GaN surfaces, supporting the use of hydrophobic surfaces composed of microstructures for UV sensing with higher sensitivity in low-temperature environments.