Gas sensitivity of silicon carbide-based diode structures

Modification of the electrophysical characteristics of Pt/6H-SiC by hydrogen treatment is investigated. It is found that the change in the bias voltage of a Pt/6H-SiC structure for a fixed capacitance is related to the hydrogen concentration by the Nernst equation. The sensor response at 150 °C is 39 mV per decade of variation of the hydrogen concentration. The changes in the forward and reverse currents and the differential resistances of the diode structure in a hydrogen-containing atmosphere are calculated. The shift of the current-voltage characteristic toward negative voltages and the decrease in the differential resistance of the junction are caused by a decrease in the height of the potential barrier of the Schottky barrier as a result of dissociative adsorption of hydrogen with the formation of a double charged layer at the metal-semiconductor boundary. At a working temperature around 150 °C the characteristics of the structures are stable. We also investigated the effect of a temperature anneal (500 °C). The formation of platinum silicides at this temperature leads to degradation of the gas-sensitive properties of the metal-semiconductor junction.