Defect induced charge trapping in C-doped a-Al_2O_3

摘要

The charged defect states of C-doped α-Al_2O_3 are investigated systematically with the density functional theory to study their thermodynamic stability and possible effects on the crystal structure and electrical conductivity. Our results reveal that under reducing (Al-rich) synthesis conditions, the most stable defect configuration is C_O~(-2) with a deep (-1|-2) thermodynamic transition level. As a result, C defects are expected to act as double acceptors by introducing appreciable deep electron traps in the host band gap of α-Al_2O_3. These results are consistent with the proposal that a large number of F~+-centers are formed as charge compensators to C_O~(-2)ions in α-Al_2O_3.