Ohmic contacts to n-type GaN using Pd/Al metallization

Ohmic contacts to n-type GaN grown by metalorganic chemical vapor deposition were formed using a Pd/Al-based metallization. Ohmic contact resistances and specific contact resistances were investigated as a function of rapid thermal annealing temperature, Pd interlayer thickness, and annealing time. As-deposited Pd/Al was found to produce rectifying contacts while the metallization exhibited ohmic characteristics after annealing at temperatures as low as 400 degrees C. A minimum contact resistance of 0.9 ohm-mm (specific contact resistance 1.2 x 10(-5) ohm-cm(2)) was obtained upon annealing at 650 degrees C for 30 s. For comparison, Al and Ti/Al contacts were also investigated. Auger electron spectroscopy, secondary ion mass spectrometry, and x-ray diffraction were used to investigate metallurgical reactions.