Improved Ohmic Contact Performance on Undoped AlGaN/GaN HEMTs Using by Ternary Alloy Predeposition

Abstract

In this paper, we have proposed a novel ohmic contact on undoped AlGaN/GaN heterostructures using the ternary SixTiyAl alloy pre-deposition ohmic contacts to reduce the contact resistance (RC) and improve the ohmic surface morphology. The use of ternary alloys simultaneously achieves n-type doping of barrier material by thermal annealing of Si and uniform Ti/Al contact with semiconductors. The systematical investigation of the parameters, including the pre-deposition layer and annealing temperature, have been performed. Low contact resistance of 0.34 Ω'mm and a specific resistivity (ρC) of 2.9 × 10−6 Ω.cm2 was achieved for the proposed metal scheme annealed at 900°C, which was superior compared with conventional Ti/Al/Ni/Au ohmic contacts (8.3 × 10−6 Ω.cm2, 0.56 Ω.mm). Atomic force microscope (AFM) compares the surface root mean square (RMS) roughness of the varied samples at the different annealing temperature. Through the results presented here, the ternary alloyed layer has significant advantages over monolayer Si or reference sample. These results are believed to facilitate the process of the GaN HEMT applied for next-generation communication systems.