First-Principles Study on III-Nitride Polymorphs: AlN/GaN/InN in the Pmn2(1) Phase

The structural, mechanical, and electronic properties, as well as stability, elastic anisotropy and effective mass of AlN/GaN/InN in the Pmn2(1) phase were determined using density functional theory (DFT). The phonon dispersion spectra and elastic constants certify the dynamic and mechanical stability at ambient pressure, and the relative enthalpies were lower than those of most proposed III-nitride polymorphs. The mechanical properties reveal that Pmn2(1)-AlN and Pmn2(1)-GaN possess a high Vickers hardness of 16.3 GPa and 12.8 GPa. Pmn2(1)-AlN, Pmn2(1)-GaN and Pmn2(1)-InN are all direct semiconductor materials within the HSE06 hybrid functional, and their calculated energy band gaps are 5.17 eV, 2.77 eV and 0.47 eV, respectively. The calculated direct energy band gaps and mechanical properties of AlN/GaN/InN in the Pmn2(1) phase reveal that these three polymorphs may possess great potential for industrial applications in the future.