Theoretical evidence for the semi-insulating character of AlN

We present ab initio density-functional calculations for acceptors, donors, and native defects in aluminum nitride, showing that acceptors are deeper (Be∼0.25 eV, Mg∼0.45 eV) and less soluble than in GaN; at further variance with GaN, both the extrinsic donors SiAl and CAl, and the native donor VN (the anion vacancy) are found to be deep (about 1 to 3 eV below the conduction). We thus predict that doped AlN will generally turn out to be semi-insulating in the normally achieved Al-rich conditions, in agreement with the known doping difficulties of high-x AlxGa1−xN alloys.