GaN Optical Devices Integrated With Sol-Gel Films for pH Detection

Accurate pH measurement is essential in numerous applications; however, developing a compact pH-sensing unit with features of quick response, a wide measurement range, and high reliability remains a significant challenge. In this work, the miniaturized design and fabrication of a fully integrated device for pH detection are demonstrated. The capabilities of the GaN device in light emission and light detection are investigated, and the effectiveness of the sol-gel film in responding to pH changes is determined through optical reflectance spectroscopy. By using an optimized film thickness of 16 \mu m, the compact integrated device exhibits a highly linear response across a wide pH range of 5-13. Dynamic measurements confirm that the device can provide consistent, stable, and fast photocurrent responses within 3-5 s when testing various 1- \mu L acid-base samples. The developed chip-scale device has appealing characteristics such as millimeter-scale size, short measurement time, low sample volume demands, and ease of use, which render it a viable candidate for pH detection applications.