Investigation of Electron-Irradiation Damage in Silicon Carbide by Hall-Effect Measurements

Abstract

We review changes of the majority-carrier concentration and mobility in SiC by irradiation of high-energy electrons using Hall-effect measurements, instead of deep level transient spectroscopy (DLTS) that can detect changes of defect densities much lower than the majority-carrier concentration. The hole concentration (p) in Al-doped p-type SiC was decreased by irradiation of electrons with over 150 keV.  This decrement of pis found to result from a decrement of Al acceptors with an acceptor level (E_A) of E_V+0.22eV, not from a creation of defects or hole traps, e.g., C vacancies.  Because irradiation of electrons with approximately 200 keV can displace only C atoms at lattice sites, neither Si nor Al atoms, one of four C atoms bonded with an Al atom at a Si-sublattice site is displaced by the irradiation, resulting that the Al atom at the Si-sublattice site cannot behave as a shallow acceptor, and is changed to a deep acceptor with E_Aof E_V+0.38eV. Compared with a large decrement of p, the degradation of the hole mobility is small. In N-doped n-type SiC, the density of N donors at hexagonal C-sublattice sites (N_NH) with a donor level (E_D) of E_C-0.07eV is reduced much more than the density of N donors at cubic C-sublattice sites (N_NK) with E_Dof E_C-0.12eV. As a result, the decrement of the electron concentration in N-doped n-type SiC by electron irradiation comes mainly from a decrement of N_NH.