First-Principles Study on III-Nitride Polymorphs: AlN/GaN/InN in the Pmn2₁ Phase

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• III-nitride materials are crucial for optoelectronic and electronic devices.
• Exploring novel polymorphs is essential for advancing material properties.
• The Pmn21 phase of AlN, GaN, and InN has not been extensively studied.

Purpose of the Study:

• To determine the structural, mechanical, electronic, and stability properties of AlN, GaN, and InN in the Pmn21 phase.
• To assess the potential of these materials for industrial applications.
• To compare the Pmn21 phase with other III-nitride polymorphs.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Phonon dispersion spectra and elastic constants were computed to evaluate stability.
• Vickers hardness and energy band gaps were calculated using the HSE06 hybrid functional.

Main Results:

• The Pmn21 phase of AlN, GaN, and InN demonstrates dynamic and mechanical stability at ambient pressure.
• Calculated relative enthalpies are lower than most proposed III-nitride polymorphs.
• Pmn21-AlN and Pmn21-GaN exhibit high Vickers hardness (16.3 GPa and 12.8 GPa).
• All three materials are direct semiconductors with HSE06 band gaps of 5.17 eV (AlN), 2.77 eV (GaN), and 0.47 eV (InN).

Conclusions:

• The Pmn21 phase of AlN, GaN, and InN possesses favorable mechanical and electronic properties.
• These materials show significant potential for future industrial applications.
• The Pmn21 phase represents a promising structural configuration for III-nitride materials.