Contacts consisting of various single layer metals to n-type GaN have been formed and characterized. The current-voltage characteristics were measured for 17 different metals (Sc, Hf, Zr, Ag, Al, V, Nb, Ti, Cr, W, Mo, Cu, Co, Au, Pd, Ni, and Pt) deposited on the same epitaxial growth layer. The barrier height, ideality factor, breakdown voltage, and effective Richardson coefficients were measured from those metals which exhibited strong rectifying behavior. The barrier heights for these metal contacts were measured using current-voltagetemperature and capacitance-voltage techniques. It was found that an increase in metal work function correlated with an increase in the barrier height. The surface state density of GaN was approximated to be very similar to CdS and almost a factor of ten less than GaAs.

Schottky barriers of Ti, Cr, Au, Pd, Ni and Pt on n-type GaN epitaxial layers grown by low-pressure metal-organic chemical vapour deposition on sapphire have been fabricated and characterized. Measurements were carried out using current-voltage (I -V ), current-voltage-temperature (I -V -T ) and capacitance-voltage (C -V ) techniques. A modified Norde plot was used as one of the analysis tools for the I -V -T measurements. The barrier heights, ideality factors and effective Richardson constants are presented. Barrier heights of 0.88, 0.92, 0.99 and 1.08 eV for Au, Pd, Ni and Pt respectively were obtained from the modified Norde plot. Contacts of Ti and Cr exhibited only slightly rectifying characteristics. These results show that the barrier height on n-GaN increases monotonically, but does not scale proportionately, with increasing metal workfunction.

The effects of reactive ion etching n-GaN surfaces with both SiCl 4 and Ar plasmas have been investigated using transmission line measurements. The measurements were made from ohmic contacts consisting of Al (as-deposited) and Ti/Al (as-deposited and rapid thermal annealed). The contact resistance, specific contact resistance, and sheet resistance were investigated as functions of the dc plasma self-bias voltage and etch time. The contact resistance extracted from contacts fabricated on surfaces etched with SiCl 4 was found to be improved over the unetched samples for all conditions investigated. Dry etching the surface with Ar severely degraded the contact resistance over the unetched sample except at the lower self-bias voltages. Rapid thermal annealing of etched samples prior to Al deposition was found to be effective in removing some of the reactive ion etching/SiCl 4 -induced damage.

Chemically assisted ion beam etching (CAIBE) characteristics of gallium nitride (GaN) have been investigated using a 500-eV Ar ion beam directed onto a sample in a Cl2 ambient. Enhanced etch rates were obtained for samples etched in the presence of Cl2 over those etched only by Ar ion milling at a substrate temperature of 20 °C. The CAIBE etch rates were further enhanced at higher substrate temperatures whereas etch rates for Ar ion milling were not influenced by substrate temperature. Etch rates as high as 210 nm/min are reported. The etch rates reported here are the highest so far reported for GaN. Anisotropic etch profiles and smooth etched surfaces in GaN have been achieved with CAIBE.

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