Response of Gallium Nitride Chemiresistors to Carbon Monoxide is Due to Oxygen Contamination

We report on the influence of oxygen impurities on the gas sensing properties of gallium nitride (GaN) chemiresistors. As shown by XRD, elemental analysis, and TEM characterization, surface oxidation of GaN for example, upon contact to ambient air atmosphere creates an oxidative amorphous layer which provides the sites for the sensing toward CO. Treating this powder under dry ammonia at 800 degrees C converts the oxide layer in nitride, and consequently the sensing performance toward CO is dramatically reduced for ammonia treated GaN gas sensors. Hence the response of GaN sensors to CO is caused by oxygen in the form of amorphous surface oxide or oxynitride.