Ohmic contact formation to GaN by Si+ implantation doping: Retarding layer, implantation fluence, encapsulation, and activation annealing temperature studies

Abstract

The aspects of Si+ implantation for low resistivity ohmic contact formation to gallium nitride (GaN) with moderate annealing temperatures for dopant activation were studied: encapsulation layer and temperature for activation annealing, and implantation fluence. The uniqueness of our approach was to implant GaN through a SiO2 retarding layer, which shifted the dopant distribution, allowing us to obtain a quasi-uniform Si profile with just one implantation. The retarding layer was extensively studied both theoretically and experimentally and its applicability for the formation of good ohmic contacts was presented. We characterized GaN after Si doping by electrical and structural methods, the latter supported by depth profiles of point and extended defects, calculated by McChasy simulation code based on measured Rutherford Backscattering/channeling spectra. Implantation with 250 keV Si+ to the effective fluence of 1.1×1016 cm−2 allowed us to obtain the best electrical parameters, sheet resistances RSH ≲ 50 Ω/sq. and specific contact resistance RC ≲ 0.1 Ω⋅mm and ρC ≈ 2×10−7 Ω⋅cm2, although there were still defects present.