| Summary: | Despite III-nitride and silicon carbide being the materials of choice for a wide range of applications, theoretical studies on their quaternary alloys are limited. Here, we report a systematic computational study on the electronic structural properties of (SiC)<i><sub>x</sub></i> (AlN)<sub>1−<i>x</i></sub> and (SiC)<i><sub>x</sub></i> (AlN)<sub>1−<i>x</i></sub> quaternary alloys, based on state-of-the-art first-principles evolutionary algorithms. Trigonal (SiCAlN, space group <i>P</i>3m1) and orthorhombic (SiCGaN, space group <i>P</i>mn2<sub>1</sub>) crystal phases were as predicted for <i>x</i> = 0.5. SiCAlN showed relatively weak thermodynamic instability, while that of SiCGaN was slightly elevated, rendering them both dynamically and mechanically stable at ambient pressure. Our calculations revealed that the <i>P</i>m31 crystal has high elastic constants, (<i>C</i><sub>11</sub>~458 GPa and <i>C</i><sub>33</sub>~447 GPa), a large bulk modulus (<i>B</i><sub>0</sub>~210 GPa), and large Young’s modulus (<i>E</i>~364 GPa), and our results suggest that SiCAlN is potentially a hard material, with a Vickers hardness of 21 GPa. Accurate electronic structures of SiCAlN and SiCGaN were calculated using the Tran–Blaha modified Becke–Johnson semi-local exchange potential. Specifically, we found evidence that SiCGaN has a very wide direct bandgap of 3.80 eV, while that of SiCAlN was indirect at 4.6 eV. Finally, for the quaternary alloys, a relatively large optical bandgap bowing of ~3 eV was found for SiCGaN, and a strong optical bandgap bowing of 0.9 eV was found for SiCAlN.
|
|---|