Sensing operations based on hexagonal GaN microdisks acting as whispering-gallery mode optical microcavities.

Using room temperature photoluminescence measurements, we have demonstrated a sensing operation based on hexagonal GaN microdisks with a side length of approximately 1.5 μm that acted as optical microcavities. In the experiment, the optical microresonant systems based on the whispering-gallery mode (WGM) in the microdisks were affected by their ambient conditions, resulting in shifts of the lasing wavelength by varying the mixing ratios of isopropanol and o-xylene. We also obtained such shifts for aqueous solutions with varying sucrose concentrations. In addition, we demonstrated that tiny waterborne particles can be detected using a microdisk. These results indicate that the WGM in the hexagonal GaN microdisks potentially can be used to develop optical microbiosensors that can evaluate a limited area with a radius of 1-2 μm.