The role of oxygen in hydrogen sensing by a platinum-gate silicon carbide gas sensor: An ultrahigh vacuum study

We report several experiments under ultrahigh vacuum conditions that elucidate the role of oxygen in the functioning of silicon carbide field-effect gas sensors with nonporous platinum gates. The devices studied are shown to be sensitive both to hydrogen and to propene. All of the results are consistent with oxygen acting through its surface reactions with hydrogen. Three specific aspects are highlighted: the need, under some conditions, for oxygen to reset the device to a fully hydrogen-depleted state; competition between hydrogen oxidation and hydrogen diffusion to metal/oxide interface sites, leading to steplike behavior as a function of the oxygen:hydrogen ratio (λ-sensing); and the removal of sulfur contamination by oxygen.