Response transients in a Pd–Ni/AlN/n-Si hydrogen sensor

The response transient from Pd and Pd–Ni alloy gated MIS hydrogen sensors with AlN as the insulating layer is investigated. Often we observe two distinct components of the transient response after switching on (or off) the hydrogen. On turn on, the initial rise of the response is followed by an overshoot which then slowly decays to the final steady state signal. We call the combination of the overshoot with this latter decay, the reverse transient. Some of our data also show a symmetric transient after hydrogen turn off. This paper presents results of a study of reverse transients observed in our devices. The temperature dependence of these reverse transient decay rates allows the estimate of the corresponding activation energies as 90 kJ/mol and 110 kJ/mol, respectively, for Pd and Pd–Ni gated devices. The closeness of these values suggests that the underlying mechanism is independent of the nature of the gate. A possible mechanism might be associated with the redistribution of low mobility negative charges within the AlN.