Phonon and electronic properties of semiconducting silicon nitride bilayers

TL;DR

This study predicts three stable 2D silicon nitride bilayers with tunable electronic properties, including band gaps and insulator-metal transitions under strain, highlighting their potential for electronic and spintronic applications.

Contribution

The paper introduces three new stable silicon nitride bilayer phases with detailed electronic and phononic properties, including strain-induced phase transitions.

Findings

All three bilayers are semiconductors with indirect band gaps from 0.25 eV to 2.92 eV.

Only s and p orbitals contribute to electronic states, with pz orbitals dominating near the Fermi level.

Biaxial strain of 16% induces insulator-metal transitions in $eta$-Si$_{2}$N$_{2}$ and $eta$-Si$_{2}$N$_{2}$.

Abstract

The two-dimensional (2D) IV-V semiconductors have attracted much attention due to their fascinating electronic and optical properties. In this work, we predicted three phases of silicon nitrides, denoted $\alpha$-Si$_{2}$N$_{2}$, $\beta$-Si$_{2}$N$_{2}$, and $\gamma$-Si$_{4}$N$_{4}$, respectively. Both $\alpha$-Si$_{2}$N$_{2}$ and $\beta$-Si$_{2}$N$_{2}$ consist of two buckled SiN sheets, and $\gamma$-Si$_{4}$N$_{4}$ consists of two puckered SiN sheets. It is challenging to transform between $\alpha$-Si$_{2}$N$_{2}$ and $\beta$-Si$_{2}$N$_{2}$ because of the high energy barrier. The three dynamically stable bilayers are semiconductors with fundamental indirect band gaps from 0.25 eV to 2.92 eV. As expected, only the s and p orbitals contribute to the electronic states, and the pz orbitals dominate near the Fermi level. Furthermore, insulator-metal transitions occur in $\alpha$-Si$_{2}$N$_{2}$ and $\beta$-Si$_{2}$N$_{2}$ under the biaxial strain of 16%. These materials perhaps have potential applications in microelectronics and spintronics.