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Two-Dimensional Wide-Band-Gap II-V Semiconductors with a Dilated Graphene-like Structure

Since the advent of graphene, two-dimensional (2D) materials become very attractive and there is growing interest to explore new 2D beyond graphene. Here, through density functional theory (DFT) calculations, we predict 2D wide-band-gap II-V semiconductor materials of M$_3$X$_2$ (M=Zn, Cd and X=N, P, As) with a dilated graphene-like honeycomb structure. The structure features that the group-V X atoms form two X-atomic planes symmetrically astride the centering group-IIB M atomic plane. The 2D Zn$_3$N$_2$, Zn$_3$P$_2$, and Zn$_3$As$_2$ are shown to have direct band gaps of 2.87, 3.81, and 3.55 eV, respectively, and the 2D Cd$_3$N$_2$, Cd$_3$P$_2$, and Cd$_3$As$_2$ exhibit indirect band gaps of 2.74, 3.51, and 3.29 eV, respectively. Each of the six 2D materials is shown to have effective carrier (either hole or electron) masses down to $0.03\sim 0.05$ $m_0$. The structural stability and feasibility of experimental realization of these 2D materials has been shown in terms of DFT phonon spectra and total energy comparison with related existing bulk materials. On the experimental side, there already are many similar two-coordinate structures of Zn and other transition metals in various organic materials, which can be considered to support our DFT prediction. Therefore, these 2D semiconductors can enrich the family of 2D electronic materials and may have promising potential for achieving novel transistors and optoelectronic devices.