Optimization of AlGaN/GaN HEMT Ohmic Contacts
for Improved Surface Morphology with Low Contact Resistance
Keywords: GaN HEMT, Ohmic metal contact, Contact resistance, Surface morphology.
Good ohmic contacts with both low contact resistance and smooth surface morphology are required for the development of a robust manufacturing process of AlGaN/GaN based high power, high frequency MMICs. This extended abstract provides an optimization of the Ti/Al/Ni/Au ohmic metal stacks on AlGaN/GaN HEMT structures with a focus on the thickness of Ni and Au layer. It is found that the Ni thickness is the dominant factor to affect the contact resistance, while the Au thickness affects the surface morphology significantly. An optimal metal stack including a thick Ni and thin Au layer is found, which produces a low contact resistance around 0.26 ohm_mm and a smooth surface morphology with a surface roughness of 22nm. An excellent edge acuity is observed. Initial device results from optimized ohmic metal stack are also discussed.