III-Nitride Turbidity Microsensor With an Ultrawide Measurement Range

In this work, a turbidity microsensor based on a GaN-on-sapphire optoelectronic device is demonstrated. The monolithic device consists of GaN diodes responsible for emitting and detecting light, enabling the detection of liquid turbidity. The integration of a hydrophobic coating on the sapphire interface can effectively eliminate the interference from refractive index variations of the tested liquid. The coated device is capable of detecting the scattered light induced by turbidity in the tested solution, exhibiting a highly linear response to turbidity throughout an ultrawide range from 0 to 10 000 nephelometric turbidity unit (NTU). Experimental measurements demonstrate the sensor with a fast response time of 123 ms and a recovery time of 143 ms, as well as its high stability over 1000 cycles. The compact design, user-friendly operation, and high stability of the sensor render it a feasible option for turbidity detection in diverse circumstances.