The effect of temperature on the forward bias electrical characteristics of both pure Ni and oxidized Ni/Au Schottky contacts on n-type GaN: A case study

The forward bias current-voltage (I-V) characteristics of both oxidized Ni/Au and pure Ni metal Schottky contacts on n-type GaN have been investigated in the temperature range 160-400 K. The I-V curves were fitted using thermionic emission (TE) theory. It was found that the zero-bias barrier height (phi(b0)) decreases while the ideality factor (eta) increases with decreasing temperature (i.e. T-0 effect). As a result, various transport models are considered in the analysis of the I-V experimental data in order to explain the observed anomaly in eta and phi(b0). The deviation from linearity in the T-0 effect plot for oxidized Ni/Au can be explained in terms of Schottky barrier height (SBH) inhomogeneity. As a result, a linear correlation between the zero-bias barrier height and ideality factor at different temperatures was found using Tung's theoretical approach in order to extrapolate the homogenous barrier height (phi(hom)). For oxidized Ni/Au, it was found that there are two distinct phi(hom) values with one representing the low temperature range (phi(hom_1) = 1.02 eV) and another representing the high temperature range (phi(hom_2) = 1.23 eV). However, for pure Ni, there is no inhomogeneity in the barrier height (i.e. phi(hom) = 0.87 eV). Furthermore, the phi(b0-ap) vs. q/(2kT) plot also shows evidence of a Gaussian distribution of barrier heights for both oxidezed Ni/Au (phi(b0-mean) = 1.45 eV and sigma(s) = 141 mV) and pure Ni (phi(b0-mean) = 0.92 eV and sigma(s) = 69.3 mV). The 1/eta vs. 1000/T plot is constructed to investigate the different current transport mechanisms in both oxidized Ni/Au and pure Ni. These various current transport mechanisms at different temperatures can be attributed to the barrier inhomogeneity at the metal-semiconductor interface.