Direct and Continuous Liquid-Level Sensing Using Gallium Nitride Ultraviolet Photodetectors

A liquid-level sensor using a gallium nitride (GaN) ultraviolet (UV) photodetector was successfully demonstrated. As the liquid level was changed, the intensity of UV light on the GaN surface was varied owing to the refraction of light on the liquid surface. For the fabrication of the liquid-level sensor, facile and rapid manufacturing was employed, involving metal wire bonding on the semiconductor surface. To characterize the fabricated sensor, the water level in the cylinder was measured according to the photocurrent change of the GaN UV photodetector. The responsivity of the liquid-level sensor depended on the diameter of the cylinder, applied voltage, and emission angle of the UV source. In particular, a cylinder diameter of 16 cm and an emission angle of 45° yielded a resolution of 0.05 cm up to the water level of 10 cm. The results of this study confirm the feasibility of liquid-level sensors for continuous and simultaneous liquid-level monitoring in harsh environments, including high-temperature plants, nuclear reactors, and chemical tanks.