P-type conductivity is normally produced in silicon carbide by doping with Al or B. The aluminum atom substitutes for silicon in the SiC lattice. Several studies have shown that nitrogen, which substitutes for carbon atoms and produces n-type conductivity in SiC, sits at the two inequivalent lattice sites in 4H-SiC, and two N activation energies of 53 meV (h) and 100 meV (k) have been reported.
Hall effect measurements and infrared absorption studies of SiC doped with Al showed only one Al activation energy, however, and the published Al activation energy in SiC (3C, 4H, and 6H) ranges from 191 meV to 280 meV. This has lead to the general conclusion that the activation energy of Al acceptors in SiC does not depend on the polytype or on the lattice site occupied.
Thermal Admittance Spectroscopy (TAS) has been used to determine the activation energy of Al in 4H-SiC specimens where NA-ND ranged from 7.2 × 1015 cm2to 5.6 × 1018 cm−2. By analogy to B in 6H-SiC, we propose two levels for Al in 4H-SiC at Ev + 0.212 eV and Ev + 0.266 eV.