First-principles investigation of point defects in Al 0.75 Ga 0.25 N: energy states and microscopic characteristics

Abstract Point defects degrade the crystal quality and optoelectronic characteristics of Al 0.75 Ga 0.25 N. To reveal the formation characteristics of point defects in Al 0.75 Ga 0.25 N, first-principles calculations are employed to systematically investigate the intrinsic features of point defects in Al 0.75 Ga 0.25 N. Formation energy calculations demonstrate that point defects form more readily in Al x Ga 1− x N with increasing Al mole fraction. Furthermore, C N , V Ga –O N , and H i possess the lowest formation energies, indicating these three defects are thermodynamically preferable to form in Al 0.75 Ga 0.25 N. For such three dominant defects, the charge distribution and crystal orbital Hamilton population are comprehensively analyzed. By comparing the bonding configurations of point defects in Al 0.5 Ga 0.5 N, it is found that the bond lengths between defects and their neighboring atoms increase with rising Al composition, and H i enables the formation of strong covalent N–H bond with surrounding N atom. Distinct from C N and H i , V Ga – O N introduces a shallow impurity level in the band gap of Al 0.75 Ga 0.25 N, which is mainly contributed by O–2p orbital. Moreover, the C–2p orbital of antisite C atom and the H–1s orbital of interstitial H atom both partially contribute to the VB (valence band), demonstrating that C N and H i are acceptors. Such defects can supply holes to the VB, thus contributing to the p-type doping of Al 0.75 Ga 0.25 N. Phonon dispersion calculations exhibit no imaginary frequencies for C N and V Ga –O N , verifying that C N and V Ga –O N stay at local energy minima within the host lattice. Moreover, the binding energy of complex point defects is discussed.