High-Resolution AlGaN/GaN HEMT-Based Electrochemical Sensor for Biomedical Applications

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Abstract
We have investigated the characteristics of pH and salinity sensor derived from the gated AlGaN/GaN high-electron mobility transistor (HEMT) structures in phosphate buffer saline (PBS) and aqueous salt solutions (NaCl + DI). In deionized (DI) water, the HEMT device showed good drain I-V characteristics, which is very close to the output characteristics of the typical HEMT structures subjected to the air. We observed a significant change in the output drain characteristics curves concerning to the variation in the pH values of PBS solutions, signifying the subsequent potential variation at the AlGaN surface. The output drain current recorded at Vds= +1 V was linearly decremented with the pH value. A high sensitivity of 4.32 μA/mm-pH was obtained. These GaN HEMT structures demonstrated a quick response to the pH changes. It was also investigated that the devices were susceptible toward the aqueous salt solution (NaCl + DI). The percentage change in drain current linearly decreased with decreasing NaCl molar concentration in DI water. We have reported on the change in current with the smaller range of molar concentration of NaCl present in water. Evaluating the sensitivity and response time, we obtained a high sensitivity of 6.48 mA/mm-molar and a response time of 250-350 ms at Vds= +1 V. We have also reported on the change in current with the molar concentration of NaCl present in PBS with a high sensitivity of 2.02 mA/mm-molar at Vds= +5 V. These outcomes show that the AlGaN/GaN HEMTs are exceptionally promising as a high-sensitivity pH sensor and salinity sensor for biological experiments.

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