Ohmic contact using the Si nano-interlayer for undoped-AlGaN/GaN heterostructures

Excellent ohmic characteristics for undoped-AlGaN/GaN heterostructures have been achieved by using a Si nano-interlayer: a 1-nm Si layer has been evaporated followed by Ti/Al/Mo/Au evaporation. A contact transfer resistance of 0.18 Ω-mm and a specific contact resistivity of 1 � 10 −6 Ω-cm 2 have been achieved along with excellent surface morphology at an optimized annealing temperature (800�C). Both ohmic contact characteristics and surface morphology are significantly better than those obtained without the Si nano-interlayer. Auger depth profiles and temperature-dependent current-voltage characteristics were investigated to understand ohmic formation. It is suggested that titanium silicide formation at the interface during rapid thermal annealing lowers the barrier height and enhances thermionic emission current.