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 similar to 0.25 eV, Mg similar to 0.45 eV) and less soluble than in GaN ; at further variance with GaN, both the extrinsic donors Si-Al and C-Al, a nd the native donor V-N (the anion vacancy) are found to be deep (about 1 t o 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 alloy s. (C) 1999 American Institute of Physics. [S0021-8979(99)06802-4].