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.
Categories: cond-mat.mtrl-sci