Low resistivity ohmic contact to n-type poly-GaN using a Ti/Au/Ni/Au multilayer metal system

A low resistivity ohmic contact to poly-GaN was achieved using the multilayer metal combination of Ti (50 Å)/Au (100 Å)/Ni (100 Å)/Au (3000 Å). Exactly how rapid thermal annealing (RTA) affects the specific contact resistivity (ρc) was also studied by varying the temperature and duration of annealing. An improvement in ρc of over one order of magnitude was achieved over the as-deposited condition with good reproducibility by RTA treatment for a total duration of 120 s. In particular, by optimizing the annealing temperature to 400 °C a relatively low ρc of 1.6 × 10−5 Ω cm2 was yielded for the contact of Ti/Au/Ni/Au to poly-GaN with a carrier concentration of (5–6) × 1017 cm−3. Related mechanism for the improvement in ρc was discussed based on the results obtained from X-ray diffraction analysis and transmission electron microscopy observations.