The presence of oxygen in the annealing environment can exhibit a strong influence on the activation of p-GaN, as demonstrated by experiments described in this letter. We activated p-GaN at 600–900 °C in four environments: ultrahigh purity (UHP) N2 gettered to remove residual O2, UHP N2 without gettering, 99.5% UHP N2/0.5% UHP O2, and 90% UHP N2/10% UHP O2. The resistivity of the p-GaN was lowest when O2 was intentionally introduced during activation and was highest when extra care was taken to getter residual O2 from the annealing gas. The experiments also demonstrate that unintentionally incorporated O2 can be at high enough levels to influence the activation process.

Ohmic contacts to p-type InGaSb have been investigated. The factors that influence the contact resistance, thermal stability, and shallowness of the contacts are examined. The most desirable contact studied in this work employs three layers. A very thin layer of palladium is deposited on the p-InGaSb first and is found to lower the resistance at the metal/semiconductor interface. The next layer is W, which is predicted to be in thermodynamic equilibrium with InGaSb and which serves as a diffusion barrier to protect the semiconductor from the reaction with the final capping layer. The final capping layer is a 100 or 150 nm Au layer. The Au lowers the metal sheet resistance, which we have found both experimentally and through modeling to influence the contact resistance measurements, and the Au layer provides a contact surface that does not oxidize. The contact resistance of the as-deposited Pd/W/Au (5/50/145 nm) contact is 0.08 Ω mm (corresponding to a specific contact resistance of <3×10−7 Ω cm2), while the more thermally stable Pd/W/Au (5/145/100 nm) contact exhibits a contact resistance of 0.08 Ω mm only after annealing at 250 °C for 3 h, in both cases on a p-In0.25Ga0.75Sb layer with a semiconductor sheet resistance of approximately 300 Ω/□. The thermal stability of the Pd/W/Au contacts was also examined. The Pd/W/Au (5/145/100 nm) contacts remained shallow and exhibited no measurable electrical degradation when aged at 250 °C in N2 for 100 h, while they survived at 250 °C for 14 days in sealed, evacuated, quartz tubes.

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Ni, Pd, and Au Ohmic contacts to p-Al0.45Ga0.55N have been examined. We have observed that annealing the contacts in excess of 800°C is required to minimize the contact resistivity. However, the Pd and Au contacts annealed in excess of 700°C, which showed much better transport properties than Ni contacts annealed at the same temperatures, suffered from a rapid photoinduced degradation of both the current-voltage characteristics of the contacts and of the sheet resistance of the p-Al0.45Ga0.55N itself. This degradation was greatly reduced by passivating the p-Al0.45Ga0.55N surface with a SiNx film. A hypothesis is presented to describe the observed degradation.