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 nkbT/q versus kbT/q graph, where n is ideality factor, kb 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 Ec-0.62 eV with 3.3 x 10-15 cm2 capture cross section observed by both deep-level transient spectroscopy (DLTS) and lnI0 versus 1/kbT 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