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We investigate the temperature effect on the electronic band structure and optical absorption property of wide-bandgap ternary nitride MgSiN2 using first-principles calculations. We find that electron–phonon coupling leads to a sizable reduction in the indirect gap of MgSiN2, which is indispensable in understanding the optoelectronic properties of this material. Taking the bandgap renormalization into account, the bandgap of MgSiN2 determined by the quasiparticle GW0 calculations shows good agreement with recent experimental result. The predicted phonon-assisted indirect optical absorption spectra show that with increasing temperature, the absorption onset undergoes a redshift. Our work provides helpful insights into the nature of the bandgap of MgSiN2 and facilitates its application in ultraviolet optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional materials provide an ideal platform for uncovering intriguing quantum phenomena and developing nanoscale devices of versatile applications. Recently, AlSb in the double-layer honeycomb (DLHC) structure was successfully synthesized exhibiting a semiconducting nature [ACS Nano 15, 8184 (2021)], which corroborates the preceding theoretical prediction and stimulates the exploration of robust DLHC materials. In this work, we propose a Janus DLHC monolayer Al2SbBi, the dynamical, thermal, and mechanical stabilities of which are confirmed by first-principles calculations. Monolayer Al2SbBi is found to be a quantum spin Hall insulator with a topological bandgap of about 0.2 eV, which presents large spin splitting and peculiar spin texture in the valence bands. Furthermore, due to the absence of inversion symmetry, monolayer Al2SbBi exhibits piezoelectricity and the piezoelectric strain coefficients d11 and d31 are calculated to be 7.97 and 0.33 pm/V, respectively, which are comparable to and even larger than those of many piezoelectric materials, for example, MoS2 (d11 = 3.8 pm/V) and InSe (d11 = 1.98 pm/V) monolayers. Our study suggests that monolayer Al2SbBi has potential applications in spintronic and piezoelectric devices. [ABSTRACT FROM AUTHOR]

In spintronics, the embodiment of abundance availability, long spin relaxation time, complete spin-polarization and high Curie temperature (TC) in intrinsic metal-free half-metallic ferromagnets (MFHMFs) are highly desirable and challenging. In this work, employing density functional theory, we first propose a dynamically, thermally, and mechanically stable two-dimensional (2D) intrinsic MFHMF, i.e. a MoS2-like PN2 monolayer, which possesses not only completely spin-polarized half-metallicity, but also an above-room-temperature TC (385 K). The half-metallic gap is calculated to be 1.70 eV, which can effectively prevent the spin–flip transition caused by thermal agitation. The mechanism of magnetism in the PN2 monolayer is mainly derived from the p electron direct exchange interaction that separates from usual d-state magnetic materials. Moreover, the robustness of the ferromagnetism and half-metallicity is observed against an external strain and carrier (electron or hole) doping. Surprisingly, electron doping can effectively increase the Curie temperature of the PN2 monolayer. The proposed research work provides an insight that PN2 can be a promising candidate for realistic room-temperature metal-free spintronic applications. [ABSTRACT FROM AUTHOR]

In spintronics, the embodiment of abundance availability, long spin relaxation time, complete spin-polarization and high Curie temperature ( T C ) in intrinsic metal-free half-metallic ferromagnets (MFHMFs) are highly desirable and challenging. In this work, employing density functional theory, we first propose a dynamically, thermally, and mechanically stable two-dimensional (2D) intrinsic MFHMF, i.e. a MoS 2 -like PN 2 monolayer, which possesses not only completely spin-polarized half-metallicity, but also an above-room-temperature T C (385 K). The half-metallic gap is calculated to be 1.70 eV, which can effectively prevent the spin-flip transition caused by thermal agitation. The mechanism of magnetism in the PN 2 monolayer is mainly derived from the p electron direct exchange interaction that separates from usual d-state magnetic materials. Moreover, the robustness of the ferromagnetism and half-metallicity is observed against an external strain and carrier (electron or hole) doping. Surprisingly, electron doping can effectively increase the Curie temperature of the PN 2 monolayer. The proposed research work provides an insight that PN 2 can be a promising candidate for realistic room-temperature metal-free spintronic applications.