Two-dimensional P3¯m1Ca3N2, Ba3P2, and Ba3As2: Promising stable narrow-gap semiconductors for infrared and broadband photodetectors

Abstract

Exploring two-dimensional (2D) narrow-gap materials with exceptional stability and outstanding photoelectric performance has become a key focus in nano-optoelectronics. However, most existing 2D materials contain relatively large band gaps, and those with narrow band gaps tend to have inadequate stability. This study employed first-principles calculation to predict three alternative narrow-gap 2D binary group (${\mathrm{II}}_3$-${\mathrm{V}}_2$) materials in the $P\overline{3}m1$ space group: ${\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$. All these materials exhibit excellent energetic, mechanical, dynamic, and thermal stability. Their mechanical properties reveal isotropic characteristics and demonstrate excellent in-plane stiffness and flexibility. Regarding electronic properties, monolayer ${\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$ possess indirect narrow band gaps of $0.41$, $0.61$, and $0.68$ eV, respectively. Moreover, they exhibit high electron mobilities (about ${10}^3$–${10}^4{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$) and are nearly isotropic. In terms of optical properties, they demonstrate a significantly broad absorption range, spanning from the IR to visible and UV regions, with remarkably high absorption coefficients (approximately ${10}^4$–${10}^5{\mathrm{cm}}^{-1}$). Additionally, their exciton binding energies are higher than those observed in traditional bulk materials while lower than most other 2D materials, facilitating excellent light-driven performance. We propose that these alternative 2D $P\overline{3}m1{\mathrm{Ca}}_3{\mathrm{N}}_2$, ${\mathrm{Ba}}_3{\mathrm{P}}_2$, and ${\mathrm{Ba}}_3{\mathrm{As}}_2$ binary narrow-gap semiconductors will hold promising application prospects in nano-optoelectronic fields such as IR light detection, ambipolar transistors, medical imaging, electrodes, optical communication, and remote sensing.