Influence of electrical characteristics on the sensitivity of p-InP-based pseudo-Schottky diodes for NO2 monitoring in atmosphere

This article is devoted to the optimization of the electrical parameters of p-InP-based Schottky diodes realized with gold metal, in order to enhance their NO2 gas sensitivity. In the structures based on p-InP, the interface states that exist at the surface of the semiconductor are responsible for the undesirable Fermi level pinning, and the value of the Schottky barrier height (ΦB) thus becomes limited by this phenomenon. In gas sensor application, the sensitivity varies as the Schottky barrier height varies. Therefore, to reduce the effect of the Fermi level pinning, one solution is to realize a pseudo-Schottky junction: a thin opposite doping layer to that of the bulk is created between the metal and the p-InP. This can be realized by introducing a germanium (Ge) layer during the evaporation of the metal, followed by an annealing process. The mechanisms of the electrical conduction of these structures are analyzed at different temperatures. The influence of the electrical properties, namely barrier height (ΦB) and n (ideality factor) on these devices sensitivities towards NO2 are demonstrated. Through the values of the ideality factor, we investigate its influence on the conduction mechanism and on the sensitivity of the gas sensor.