V/Al/V/Ag contacts to n-GaN and n-AlGaN

Abstract

Low-resistance V/Al/V/Ag contacts have recently been reported to Al0.27Ga0.73N/GaN heterostructures with a thin GaN cap. These contacts had smooth surfaces and good edge definition. In this study, the V/Al/V/Ag metallization was adapted to other compositions of n-AlxGa1−xN, and it was found to provide low specific contact resistances as well as smooth surfaces on both n-GaN and n-Al0.58Ga0.42N. Another advantage of these contacts is that limited changes in specific contact resistance and morphology were observed when changing the metal layer thicknesses and processing conditions of the V/Al/V/Ag metallization on these semiconductors. The V (20)/Al (95)/V (20)/Ag (120 nm) contact provided a specific contact resistance of (2.1±0.9)×10−6 Ω cm2 when annealed at 825 °C for 30 s on n-GaN and a V (20)/Al (95)/V (5)/Ag (120 nm) contact provided a value of (2.4±0.3)×10−4 Ω cm2 when annealed at 875 °C for 60 s on n-Al0.58Ga0.42N. In each case, transmission electron microscopy revealed that the reaction between the semiconductor and metallization was limited and the majority of the interface was contacted by a composite of primarily Ag-bearing grains. Measurements of the specific contact resistance as a function of temperature revealed that field emission is the dominant current transport mechanism in low resistance Ohmic contacts to n-GaN and n-Al0.58Ga0.42N.