A comparative study of C plus Al coimplantation and Al implantation in 4Hand 6H-SiC

Coimplantation of equal concentrations of C and Al in 6H- and 4H-SiC has been investigated comparatively with implantation of Al alone in the Al concentration range of N_Al=8×10¹⁹ to 2×10²¹ cm^-3. C-Al coimplantation at either room temperature (RT) or 600°C, when implanted with N_Al >1×10²⁰ cm^-3, gives improvements over Al alone implantation in the specific contact resistance ρ_c, of Al ohmic contacts on the implanted surfaces. The lowest median values of ρ_c obtained are 3× and 6×10^-15 Ω cm² for 6H- and 4H-SiC, respectively. In the mid to high 10²⁰ cm^-3 N_Al range, sheet resistivity of the p-type implanted layers are also reduced by the coimplantation at RT. Temperature-dependent Hall-effect measurements reveal the correlated trends in increased impurity-band conduction and high-temperature (>400 K) hole concentration. Implantation at 600°C, by either coimplantation or Al alone implantation, degrades the electrical characteristics in the mid 10²⁰ cm^-3 N_Al range, which implies that amorphization of as-implanted layers is necessary for effective activation of Al acceptors. It will be shown that C-Al coimplantation at RT can produce p⁺-n diodes with low reverse leakage currents and high forward current capability as evidenced by the 110 A/cm² forward current density at 2.8 V and 19 nA/cm² leakage current density at -100 V for 4H-SiC p⁺-n diodes created by C-Al coimplantation at RT