Monolithic-Integrated GaN Optical Sensor to Detect the Adulterated Honey

This paper reports a monolithic-integrated GaN optical sensor to act as a suger sensor to determine the concentration of fructose in adulterated honey. In this optical sensor chip, it contains two key function devices, one is the light-emitting diode(LED) and the other is a photo detector(PD), which are monolithic integrated in one chip. It can be achieved by fabricating on a same GaN epilayer on sapphire wafer with the same InGaN/GaN multi-quantum wells. The light emitted from the LED can directly detect the liquid substance on the surface through the transparent sapphire substrate, while the PD receives the refracted light. Finally, the changes of refractive index of fructose solution and adulterated honey samples can be quantitatively reflected by the measured photocurrent signal. This novel single-chip integrated solution completely eliminates the complex assembly of external optical elements and reduces the impact of external environment on PD sensitivity. The results show that the linear relationship between the adulteration concentration and the change of photocurrent signal is -0.206 $\mu$A/% in the range of 5-25% gradient concentration. The developed microsensor has the advantages of small size, low cost, high repeatability, easy to integration and operation.