A comparative study of C plus Al coimplantation and Al implantation in 4H-and 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-AI = 8x10(19) to 2 x 10(21) cm(-3). C-Al coimplantation at either room temperature (RT) or 600 degrees C, when implanted with N-Al > 1 x 10(20) cm(-3), gives improvements over Al alone implantation in the specific contact resistance pc of Al ohmic contacts on the implanted surfaces. The lowest median values of pc obtained are 3 x and 6 x 10(-5) Omega cm(2) for 6H- and JH-S1C. respectively. Ln the mid to high 1020 cm(-3) N-AI 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 degrees C, by either coimplantation or Al atone implantation, degrades the electrical characteristics in the mid 10(20) cm(-3) N-AI range, which implies that amorphization of as-implanted Layers is necessary for effective activation of Al acceptors, It will be shown that C-AI coimplantation at RT can produce p(+)-n diodes with low reverse leakage currents and high forward current capability as evidenced by the 110 A/cm(2) forward current density at 2.8 V and 19 nA/cm(2) Leakage current density at -100 V for 4H-SiC p(+)-n diodes created by C-AI coimplantation at RT.