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

Abstract

We have investigated the current transport mechanisms in Ru/Pd/n-GaN Schottky barrier diodes in the temperature range 105–405K. The calculated barrier height and ideality factor are 0.27eV and 3.93 at 105K, and 0.75eV and 1.29 at 405K respectively, and it is observed that barrier height (Φbo) 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 (Φbo) versus 1/2kT plot yields a mean barrier height (Φ¯bo) of 0.89eV and a standard deviation (σo) of 111mV. A modified ln(I0/T2)-(q2σ02/2k2T2) versus 1000/T plot gives Φ¯bo (T=0) and A∗ as 0.87eV and 21.25A/cm2K2, 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 9.38×1013 to 1.06×1012eV−1cm−2 in the band gap below conduction band from EC-0.14 to EC-0.66eV. Deep level transient spectroscopy (DLTS) results showed that the two deep level defects are observed in as-grown sample (E1 and E2) which have activation energies of E1=0.54eV and E2=0.68eV, suggest that E2 level is most probably associated with NGa-related defect.