Influence of Thermal Annealing on Ohmic Contacts and Device Isolation in AlGaN/GaN Heterostructures

Gallium nitride (GaN) and related alloys (Al(x)Ga(1-x)N) are promising semiconductors For high-frequency and high-power devices applications. In particular, the growth of AlGaN/GaN heterostructures oil SiC Substrates, due to the high thermal conductivity of SiC, can lead to significant improvement in the device performances. Ail important issue in the fabrication of AlGaN/GaN devices is the influence of the required thermal budget (700-900 degrees C) on the properties of Ohmic contacts and device isolation. In this work, the influence of thermal annealing on the fabrication of AlGaN/GaN devices was studied. Ti/Al/Ni/Au multilayers led to ail Ohmic behavior with a specific resistance rho(c) in the 10(-5) Omega cm(2) range upon annealing between 750 degrees C and 850 degrees C. The electrical behavior of Ohmic contacts was correlated with the evolution of the formed phases and with the temperature behavior of rho(c). The stability of the inter-device isolation obtained by nitrogen-implantation during annealing at these temperatures was also monitored.