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

Abstract

High-dose aluminum-ion $\left({\mathrm{Al}}^{+}\right)$ implantation into 4H-SiC (0001) and $\left(11\overline{2}0\right)$ has been investigated. The dependences of the electrical properties on the implanted ${\mathrm{Al}}^{+}$ dose and on the annealing time were examined by Hall-effect measurements. A low sheet resistance of $2.3\mathrm{k}\Omega ∕◻$ ($0.2\mu \mathrm{m}$ deep) was obtained in a (0001) sample by implantation of ${\mathrm{Al}}^{+}$ with a dose of $3.0\times {10}^{16}{\mathrm{cm}}^{-2}$ at $500°\mathrm{C}$ and a subsequent high-temperature anneal at $1800°\mathrm{C}$ for a short time of $1\min$ . In the case of $\left(11\overline{2}0\right)$ samples, even room-temperature implantation resulted in a low sheet resistance of $2.3\mathrm{k}\Omega ∕◻$ ($0.2\mu \mathrm{m}$ -deep) after anneal at $1800°\mathrm{C}$ . 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.