Electron transport and barrier inhomogeneities in palladium silicide Schottky diodes

The current-voltage (I-V) characteristics of Schottky diodes, prepared by deposition of palladium film on to a n/n(+) silicon wafer held at 573 K, are measured over a temperature range 37-307 K and analyzed in terms of thermionic emission-diffusion (TED) theory by incorporating the concept of barrier inhomogeneities through a Gaussian distribution function. The process adopted is shown to yield an ideal Schottky diode with a near constant barrier height of 0.734 V and ideality factor 1.05 in the temperature interval 215-307 K. Below 215 K, both the barrier height (phi(bo)) and the ideality factor (eta) exhibit abnormal temperature dependence and are explained by invoking two sets of Gaussian distributions of barrier heights at 84-215 K and 37-84 K. Further, it is demonstrated that the forward bias makes the Gaussian distribution dynamic so that the mean fluctuates (i.e., increases or decreases depending on whether its voltage coefficient is positive or negative) and the standard deviation decreases progressively, i.e., the barrier homogenizes temporarily. The changes occur in such a way that the apparent barrier height at any bias is always higher than at zero-bias. Finally, it is pointed out that the presence of single/multiple distributions can be ascertained and the values of respective parameters deduced from the phi(ap) vs. 1/T plot itself. Also, the inverse ideality factor versus inverse temperature plot provides bias coefficients of the mean barrier height and standard deviation of the distribution function.