InGaN/GaN MQW optoelectronic chips for compact coffee concentration sensing

This study develops a compact InGaN/GaN multiple-quantum-well (MQW) optoelectronic platform for coffee concentration measurement. The platform consists of two wavelength-distinct MQW chips assembled in a back-to-back configuration, with the blue-band device serving as the emitter and the green-band device as the preferred photodetector. The green-band photodetector exhibits broader spectral overlap with the blue emitter, providing an optical basis for detector selection. By monitoring the zero-bias photocurrent of the detector, concentration-dependent optical changes in the sensing path are converted into an electrical signal. Over the investigated concentration range of 0%-100%, the green-detector configuration exhibits a clear concentration-dependent photocurrent response, while transient measurements at fixed 20%-80% concentrations reveal a sub-100-ms optoelectronic response, with repeated modulation showing stable operation. These results demonstrate the feasibility of the wavelength-distinct emitter-detector architecture for compact coffee concentration measurement.