Shallow acceptor levels in 4H- and 6H-SiC

Shallow impurities are the principal means of affecting the electrical properties of semiconductors in order to induce desired characteristics. They can be used to isolate a region by introducing carriers of opposite charge, or they can be used to enhance the number of carriers of a particular type. Thermal admittance spectroscopy has been used to determine the activation energies of the principal p-type dopants, Al and B, in 4H and 6H-SiC, and temperature dependent Hall effect measurements were used to study the shallow B accepters in 6H-SiC. The acceptor species B and Al occupy inequivalent lattice sites in the Si sublattice, and would be expected to exhibit distinct energy levels for each site in analogy to the well known donor energy levels of N. Activation energies for B in 6H-SiC were found to be E-h = E-v + 0.27 eV, E-k1 = E-v + 0.31 eV, and E-k2 = E-v + 0.38 eV. Al accepters in 4H-SiC were found to-exhibit-two energy levels at E-h = E-v + 0.212 eV and E-k = E-v +0.266 eV.