Current transport mechanisms in Ru/Pd/n-GaN Schottky barrier diodes and deep level defect studies

We have investigated the current transport mechanisms in Ru/Pd/n-GaN Schottky barrier diodes in the temperature range 105-405 K. The calculated barrier height and ideality factor are 0.27 eV and 3.93 at 105 K, and 0.75 eV and 1.29 at 405 K respectively, and it is observed that barrier height (Phi(bo)) decreases and the ideality factor (n) increases with decreasing temperature. The apparent barrier height and the ideality factor derived by using thermionic emission theory are found to be strongly temperature dependent. This behavior has been interpreted based on the assumption of a Gaussian distribution of barrier heights due to barrier height inhomogeneities that prevail at the metal-semiconductor interface. The linearity of the apparent barrier height (Phi(bo)) versus 1/2kT plot yields a mean barrier height ((Phi) over bar (bo)) of 0.89 eV and a standard deviation (sigma(o)) of 111 mV. A modified In(I-o/T-2) - (q(2)sigma(2)(0)/2k(2)T(2)) versus 1000/T plot gives (Phi) over bar (bo) (T=0) and A* as 0.87 eV and 21.25 A/cm(2) K-2, respectively without using the temperature coefficient of the barrier heights. The interface state densities extracted for the Ru/Pd/n-GaN Schottky diode are in the range of 9.38 x 10(13) to 1.06 x 10(12) eV(-1) cm(-2) in the band gap below conduction band from E-C-0.14 to E-C-0.66 eV. Deep level transient spectroscopy (DLTS) results showed that the two deep level defects are observed in as-grown sample (E-1 and E-2) which have activation energies of E-1 = 0.54 eV and E-2 = 0.68 eV, suggest that E-2 level is most probably associated with N-Ga-related defect. (C) 2012 Elsevier Ltd. All rights reserved.