Route to increased hole mobility GaN induced by epitaxial uniaxial strain on II-IV nitrides

GaN is a prominent semiconductor candidate for highly efficient power electronics applications. The low hole mobility in GaN, < 40 cm²/Vs, poses challenges to realizing p-type GaN devices. Applying strain to GaN has shown promise to increase hole mobility. In this first principles study, we investigate the effect of epitaxial in-plane compressive strain of GaN to the lattice constants of II-IV nitrides ZnGeN₂ and MgSiN₂ on phonon-limitted carrier mobility. Carrier mobilities are calculated by the iterative Boltzmann transport equation in the EPW code. The effective compressive strain induces inversion of the heavy hole and crystal field bands, leading to low effective hole mass dispersions in the compressive direction. We find that strain matching GaN to ZnGeN₂ or MgSiN₂ results in a 46% or 258% increase in phonon-limited hole mobility at room temperature in the compressive strain direction, respectively. While the extreme strain state induced by strain matching GaN to MgSiN₂ severely limits thin film critical thickness, we predict that epitaxial strain matching GaN to an ordered alloy Zn_0.75Mg_0.25Ge_0.75Si_0.25N₂ could still promote a mobility increase of 164% while maintaining a film critical thickness of over 8 nm, opening a pathway to high hole mobility thin film GaN devices.