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

Abstract

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/sub Al/=8/spl times/10/sup 19/ to 2/spl times/10/sup 21/ cm/sup -3/. C-Al coimplantation at either room temperature (RT) or 600/spl deg/C, when implanted with N/sub Al/>1/spl times/10/sup 20/ cm/sup -3/, gives improvements over Al alone implantation in the specific contact resistance /spl rho//sub c/, of Al ohmic contacts on the implanted surfaces. The lowest median values of /spl rho//sub c/ obtained are 3/spl times/ and 6/spl times/10/sup -15/ /spl Omega/ cm/sup 2/ for 6H- and 4H-SiC, respectively. In the mid to high 10/sup 20/ cm/sup -3/ N/sub 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/spl deg/C, by either coimplantation or Al alone implantation, degrades the electrical characteristics in the mid 10/sup 20/ cm/sup -3/ N/sub 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/sup +/-n diodes with low reverse leakage currents and high forward current capability as evidenced by the 110 A/cm/sup 2/ forward current density at 2.8 V and 19 nA/cm/sup 2/ leakage current density at -100 V for 4H-SiC p/sup +/-n diodes created by C-Al coimplantation at RT.