Ohmic contacts to Mg-doped p-GaN grown by MOCVD [1] are studied using a circular transmission line model (TLM) to avoid the need for isolation. For samples which use a p-dopant activation anneal before metallization, no appreciable difference in the specific contact resistance, r,, as a function of different capping options is observed. However, a lower r, is obtained when no pre-metallization anneal is employed, and the post-metallization anneal simultaneously activates the p-dopant and anneals the contact. This trend is shown for Pt/Au, Pt, Pd/Pt/Au, and Ni/Au contacts to p-GaN. The r 's for these metal contacts are in the range of 1.4-7.6 x 10.-ohm-cm 2 at room temperature at a bias of 1OmA. No particular metallization formula clearly yields a consistently superior contact. Instead, the temperature of the contact has the strongest influence.Detailed studies of the electrical properties of the Pt/Au contacts reveal that the I-V linearity improves significantly with increasing temperature. At room temperature, a slightly rectified I-V characteristic curve is obtained, while at 200'C and above, the I-V curve is linear. For all the p-GaN samples, it is also found that the sheet resistance decreases by an order of magnitude with increasing temperature from 25'C to 350'C. The specific contact resistance is also found to decrease by nearly an order of magnitude for a temperature increase of the same range. A minimum r, of 4.2 x 10-4 ohm-cm 2 was obtained at a temperature of 350'C for a Pt/Au contact. This result is the lowest reported r, for ohmic contacts to p-GaN.

A variety of different plasma chemistries, including SF6, Clz, IC1 and IBr, have been examined for dry etching of 6H-Sic in high ion density plasma tools (Inductively Coupled Plasma and Electron Cyclotron Resonance). Rates up to 4,500A-min-' were obtained for SF6 plasmas, while much lower rates (G300A.min") were achieved with C12, IC1 and IBr. The FZbased chemistries have poor selectivity for Sic over photoresist masks (typically 0.4-0.5), but Ni masks are more robust, and allow etch depths 2 1 0 p in the SIC. A micromachining process (sequential etch/deposition steps) designed for Si produces relatively low etch rates (<2,000A.min*') for Sic.

Electron cyclotron resonance (ECR) plasma etching characteristics of gallium nitride (GaN) are investigated using low pressure (4-10 mTorr) SiCl4/Ar and Cl2/H2/Ar ECR discharges. The purpose of this effort is to develop a dry etching process for making laser mirrors on GaN and to examine dry etching processes of GaN that do not require hydrogen, which is known to cause carrier compensation in GaN. The etch rate is found to increase near-linearly with increasing DC bias, and a minimum DC bias of 100V is required to initiate etching in SiCl4/Ar. We have also found that the material quality significantly affects the etch rate. The latter decreases with x-ray rocking curve half-width and increases with defect density. A reasonable etch rate of 660Ǻ/min and good surface morphologies obtained in SiCl/Ar ECR etching make this process suitable for gate recess of an FET. An etch rate of 5270Ǻ/min has been achieved in Cl2/H2/Ar plasmas. This is the highest reported etch rate of GaN so far. The smooth and vertical etch sidewalls (etch to mask selectivity of 16 is obtained) make this process promising for dry-etched laser mirrors on GaN.