Electrical characteristics of Ti/Al contacts on AlInN:Mg/GaN heterostructures

The electrical characteristics of a Ti/Al metal contact on Mg-doped AlInN/GaN heterostructures were investigated using a transmission line model. The as-deposited Ti/Al contact exhibited near Ohmic contact with a specific contact resistance of 1:78 × 10^-2 ωcm², while the thermal annealing performed at 600 °C led to better Ohmic contact with a contact resistance of 9:38 × 10^-4 ωcm². This could be attributed to the formation of a direct Ohmic path connecting the contact and the two-dimensional electron gas beneath an AlInN:Mg barrier upon thermal annealing, namely, a spike contact through the indiffusion of Al as verified from secondary ion mass spectroscopy. Current-voltage-temperature measurements showed an insignificant temperature dependence in both the sheet resistance and the contact resistance, which seemed to be associated with the distinctive feature of the spike contact.