High-temperature Schottky diode characteristics of bulk ZnO

Current–voltage ( I – V ) measurements of Ag/n-ZnO have been carried out at temperatures of 200–500 K in order to understand the temperature dependence of the diode characteristics. Forward-bias I – V analysis results in a Schottky barrier height of 0.82 eV and an ideality factor of 1.55 at room temperature. The barrier height of 0.74 eV and Richardson constant of 0.248 A K −2 cm −2 were also calculated from the Richardson plot, which shows nearly linear characteristics in the temperature range 240–440 K. From the nk b T / q versus k b T / q graph, where n is ideality factor, k b the Boltzmann constant, T the temperature and q the electronic charge we deduce that thermionic field emission (TFE) is dominant in the charge transport mechanism. At higher sample temperatures (>440 K), a trap-assisted tunnelling mechanism is proposed due to the existence of a deep donor situated at E c —0.62 eV with 3.3 × 10 −15 cm 2 capture cross section observed by both deep-level transient spectroscopy (DLTS) and ln I 0 versus 1/ k b T plots. The ideality factor almost remains constant in the temperature range 240–400 K, which shows the stability of the Schottky contact in this temperature range.