Abstract
Silicon carbide (SiC)-based metal-insulator-semiconductor devices are attractive for gas sensing in automotive exhausts and flue gases. The response of the devices to reducing gases has been assumed to be due to a reduced metal work function at the metal-oxide interface that shifts the flat band capacitance to lower voltages. We have discovered that high temperature (700 K) exposure to hydrogen results not only in the flat-band voltage occurring at a more negative bias than in oxygen, but also in the transition from accumulation (high capacitance) to inversion (low capacitance) occurring over a relatively narrow voltage range. In oxygen, this transition is broadened, indicating the creation of a high density of interface states. We present a model of the hydrogen/oxygen response based on two independent phenomena: a chemically induced shift in the metal-semiconductor work function difference and the passivation/creation of charged states at the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SiC interface that is much slower than the work function shift. We discuss the effect of these results on sensor design and the choice of operating point.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have