Electrical activation of high-concentration aluminum implanted in 4H-SiC

High-dose aluminum-ion (Al+) implantation into 4H-SiC (0001) and (112¯0) has been investigated. The dependences of the electrical properties on the implanted Al+ dose and on the annealing time were examined by Hall-effect measurements. A low sheet resistance of 2.3kΩ∕◻ (0.2μm deep) was obtained in a (0001) sample by implantation of Al+ with a dose of 3.0×1016cm−2 at 500°C and a subsequent high-temperature anneal at 1800°C for a short time of 1min. In the case of (112¯0) samples, even room-temperature implantation resulted in a low sheet resistance of 2.3kΩ∕◻ (0.2μm-deep) after anneal at 1800°C. The Hall data are compared with the calculated values determined by using the doping-concentration dependent ionization energy of Al acceptors. The experimentally obtained free-hole concentrations agree well with the theoretically expected values. Hole mobilities are not as high as the empirical mobilities obtained in Al-doped epitaxial layers. The differences in the electrical properties between the experimental data and expected values are discussed.