Abstract
Detection of acetone concentration in exhaled breath can be developed to diagnose diabetes as a noninvasive methods. And indium nitride (InN) epilayer, which have some special electronic property such as electron accumulation, can be used to fabricate acetone gas sensors with high sensitivity. Acetone gas sensors based on ultrathin (~10 nm) InN epilayers with and without a thin catalytic platinum (Pt) layer have been fabricated and demonstrated. The bare InN sensor exhibits a maximum response at 200 °C in air ambiences. The maximum response of current variation under 10 ppm acetone exposure in air ambience at 200 °C corresponding to 16 % ( 37.6 µA ), with a response time of 1262 s. The plot of log(△I/I0) to log(Cacetone) shows a linear relationship with a slope of 0.58 at a acetone concentration range from 0.4 ppm to 20 ppm. On the other hand, the Pt-coated InN sensor exhibits a higher response to acetone. At 200 °C, the sensor shows a high current variation ratio of 28.7 % (94 µA) and a short response time of 150 s under the same gas exposure environment. The plot of log(△I/I0) to log(Cacetone) shows a linear relationship with a slope of 0.50 at a acetone concentration range from 0.4 ppm to 20 ppm. In comparison with a bare InN sensor tested in the same conditions, the Pt catalytic layer enhances the current variation by 2.5 times. The detection limits of the sensors with and without a Pt layer are both less than 0.4 ppm. The influences of carbon dioxide and oxygen on Pt-coated InN sensors have been investigated. The current variation ratio is 4.6 % (15 µA) when oxygen concentration drop off from 21 % to 16 %, near to the current variation ratio under 0.4 ppm acetone exposure. And the current variation ratio under 5 % CO2 in air ambiance is 7.6 % (26.4 µA), near to the current variation ration under 1 ppm acetone exposure.