Effect of Cl2 plasma treatment and annealing on vanadium based metal contacts to Si-doped Al0.75Ga0.25N.

In order to understand the electrical properties of V/Al/Ni/Au metal contacts to Si-doped Al_0.75Ga_0.25N layers, X-ray photoelectron spectroscopy analysis was performed on differently treated AlGaN:Si surfaces before metal deposition, and transmission electron microscopy was used to study the semiconductor-metal interface after contact annealing at 900 °C. Cl2 plasma etching of AlGaN increases the aluminum/nitrogen ratio at the surface, and Al oxide or oxynitride is always formed by any surface treatment applied after etching. After contact annealing, a complex interface structure including amorphous AlO_x and different metal phases such as Al-Au-Ni, V-Al, and V₂N were found. The electrical properties of the contacts were determined by thermionic emission and/ or thermionic field emission in the low voltage regime. Nearly ohmic contacts on AlGaN surfaces exposed to a Cl₂ plasma were only obtained by annealing the sample at a temperature of 815 °C under N₂/NH₃ prior to metallization. By this treatment, the oxygen contamination on the surface could be minimized, resulting in a larger semiconductor area to be in direct contact with metal phases such as Al-rich Al-Au-Ni or V-Al and leading to a contact resistivity of 2.5 × 10^-2 Ωcm². This treatment can be used to significantly reduce the operating voltage of current deep ultraviolet light emitting diodes which will increase their wall plug efficiency and lower the thermal stress during their operation. [ABSTRACT FROM AUTHOR]