Strain effects on doping in AlN and GaN

Controllable doping in AlN and GaN is essential for next-generation high-power electronics and deep-ultraviolet light sources. We perform first-principles calculations to investigate strain effects on donors (Si_Al, S_N, Se_N) in AlN and on the Mg_Ga acceptor in GaN. In AlN, the (+/0) donor transition levels for S_N and Se_N  decrease under in-plane tensile strains, becoming shallow at critical strain values. The DX transition level (+/-) of Si_Al decreases to 98 meV below the conduction-band minimum (CBM) at 2.5% strain; for larger strains, the DX configuration is no longer stable and Si acts as a shallow donor. This behavior is primarily driven by the lowering of the CBM under tensile strains, with smaller additional contributions from changes in stability of the DX state. For Mg_Ga in GaN, the (0/-) acceptor transition level decreases relative to the valence-band maximum (VBM) under in-plane compressive strains. With a 1% uniaxial compression along the [1-100] direction, accompanied by 0.3% and 0.2% tensile relaxations along the orthogonal directions, the (0/−) transition level decreases by 68 meV, which can increase the hole concentration by approximately a factor of four. These results demonstrate that strain engineering offers an effective strategy to enhance doping in the wide-bandgap nitrides.

This work was supported by SRC, DARPA, and DOE.