Determining the hydrogen concentration from the photovoltage of Pd–oxide–InP MIS structures

The photovoltage of a metal–insulator–semiconductor structure (Pd–anodic oxide–InP) is studied in relation to the hydrogen concentration in the range 0.1–100 vol % in a nitrogen–hydrogen gas mixture. It is shown that, under simultaneous exposure of the structure to light and hydrogen, the photovoltage decay rate and the hydrogen concentration are exponentially related to each other: $N_{\mathrm{H}} = a\operatorname{exp}(bS)$. Here, $N_{\mathrm{H}}$ is the hydrogen concentration (vol %) in the nitrogen–hydrogen mixture. $S=dU/dt|_{t = 0}$ is the rate at which the signal U changes in the initial portion of the photovoltage decay, beginning from the instant at which the structure is brought into contact with the gas mixture. $a$ and $b$ are constants dependent on the thicknesses of the palladium layer and anodic oxide film on InP.