Characteristics of carbon monoxide sensors made by polar and nonpolar zinc oxide nanowires gated AlGaN/GaN high electron mobility transistor

AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon exposure to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition, with perfect crystal quality will attach CO molecules and release electrons, which will lead to a change of surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezo-induced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200 ppm in the open cavity with continuous gas flow using a 50 × 50 μm2 gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor, respectively.