The electrical resistivity of monolayer graphene exhibit significant changes upon
expose to different concentration of oxygen (O2) at room temperature. The monolayer
graphene, grown by chemical vapor deposition (CVD) with perfect uniformity within
1cm×1cm will attach O2 molecules which will act as a p-type dopant and enhance the
hole conductivity, make a change of resistivity of graphene thin film. We quantified
the change of resistivity of graphene versus different O2 concentration and the
detection limit of the simple O2 sensor was 1.25% in volume ratio.
AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires
modified gate exhibit significant changes in channel conductance upon expose to different
concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical
vapor deposition (CVD), with perfect crystal quality will attach CO molecule 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 piezoinduced 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 3200ppm in the
open cavity with continuous gas flow using a 50x50μm2 gate sensing area for polar and nonpolar ZnO
nanowire gated HEMTs sensor.
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