Title: Novel Phases of Semi-Conducting Silicon Nitride Bilayer: A First-Principle Study,
Abstract: In this paper, we have predicted the stabilities of several two-dimensional
phases of silicon nitride, which we name as \alpha-phase, \beta-phase, and
\gamma-phase, respectively. Both \alpha- and \beta-phases has formula
Si$_{2}$N$_{2}$, and are consisted of two similar layer of buckled SiN sheet.
Similarly, \gamma-phase is consisted of two puckered SiN sheets. For these
phases, the two layers are connected with Si-Si covalent bonds. Transformation
between \alpha- and \beta-phases is difficult because of the high energy
barrier. Phonon spectra of both \alpha- and \beta-phase suggest their
thermodynamic stabilities, because no phonon mode with imaginary frequency is
present. By Contrast, \gamma-phase is unstable because phonon modes with
imaginary frequencies are found along \Gamma-Y path in the Brilliouin zone.
Both \alpha- and \beta-phase are semiconductor with narrow fundamental indirect
band gap of 1.7eV and 1.9eV, respectively. As expected, only s and p orbitals
in the outermost shells contribute the band structures. The p$_{z}$ orbitals
have greater contribution near the Fermi level. These materials can easily
exfoliate to form 2D structures, and may have potential electronic
applications.