Fabrication and Characterization of Liquid-Phase Sensor utilizing GaN-Based Two Terminal Devices

Gallium Nitride (GaN) based materials are highly suitable for liquid‐phase sensor applications due to their chemical stability and high internal piezoelectric polarization. The sensitivity of GaN surfaces in aqueous solutions and polar liquids has been investigated. For this purpose, two terminal devices fabricated on bulk Si doped‐GaN structures and undoped‐AlGaN/GaN heterostructures with unpassivated open area are used to measure the responses to the changes of the H+ concentration in aqueous solutions and the dipole moment in polar liquids. The I–V characteristics show that the devices are able to distinguish the variations of pH. It is observed that the drain current decreases linearly with pH for both device structures. Evaluating the sensitivity in aqueous solutions at VDS = 2V, a quite large current change is obtained for both structures. For the response to polar liquids, it is also found that the drain current decreases with the dipole moments. The results indicate that both devices are capable of distinguishing molecules with different dipole moments.