Real Relationship between Acceptor Density and Hole Concentration in Al-Implanted 4H-SiC

Abstract

Al-implanted p-type 4H-SiC layers with different conditions of implantation and annealing temperatures are formed, and the temperature dependence of the hole concentration ) (T p in the p layer is obtained from Hall-effect measurements. In order to determine the reliable acceptor density ( A N ) from ) (T p , it is found that the Fermi-Dirac distribution function is not appropriate and that a distribution function including the influence of the excited states of Al acceptors is required. This is because the Al acceptor level in SiC is deep (~180 meV) and because its first excited state level, which is calculated by the hydrogenic model, is still deep (~35 meV), which is close to the acceptor level of B in Si. It is demonstrated that the proposed distribution function is suitable for obtaining the actual relationship between A N and ) (T p .