Extended Gate Field Effect Transistor-Based N-Type Gallium Nitride as a pH Sensor

The exceptional properties of gallium nitride (GaN) such as distinctive band gap and strong chemical stability make it promising as a semiconductor material to detect and select ions, liquids and gases. Sensing characteristics of an extended gate field effect transistor (EGFET)-based undoped N-type GaN as a pH sensor was investigated by using six buffer solutions with pH range 2–12 at room temperature. Distinctive current-voltage (I–V) characteristics of EGFET with gate controllability were observed in a solution. The surface potential of the membrane at the sensing area is controlled by Ag/AgCl reference electrode via aqueous solution. The sensitivity in terms of reference voltage in the linear region was 24.72 mV/pH with a good linearity. There is another function in the saturation region in the expression via drain-source current (IDS), and the outputs indicated that to 0.39 (μA)1/2/pH. IDS sensitivity proved to be a reliable outcome as a linear response along the pH range. As an indicator of the stability and the reversibility of our sensor, we measured the hysteresis with two loops. The results showed a low value of hysteresis depth of 14.98 mV and 13.06 mV for the acidic side, 30.91 and 32.72 for the basic side.