Calculations of the Specific Resistance of Contacts to III-V Nitride Compounds

We present calculations of the specific contact resistance for metals to GaN. Our calculations include a correct determination of the Fermi level taking into account the effect of the degenerate doping levels, required in creating tunneling ohmic contacts. Using a recently reported improved WKB approximation suitable in representing the depletion width at the metal-semiconductor interface, and a two band k-p model for the effective masses, specific contact resistance was determined as a function of doping concentration. The specific contact resistance was calculated using the best data available for barrier heights, effective masses and dielectric coefficients for GaN. Because the barrier height at the metal-semiconductor interface has a very large effect on the contact resistance and the available data is sketchy or uncertain, the effect of varying the barrier height on the calculated specific contact resistance was investigated. Further, since the III-V nitrides are being considered for high temperature device applications, the specific contact resistance was also determined as a function of temperature.