Single-layer group IV-V and group V-IV-III-VI semiconductors: Structural stability, electronic structures, optical properties, and photocatalysis

Recently, single-layer group III monochalcogenides have attracted both theoretical and experimental interest at their potential applications in photonic devices, electronic devices, and solar energy conversion. Excited by this, we theoretically design two kinds of highly stable single-layer group IV-V ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P) and group V-IV-III-VI ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P; $\mathrm{III}=\mathrm{Al},\mathrm{Ga}$, and In; $\mathrm{VI}=\mathrm{O}$ and S) compounds with the same structures with single-layer group III monochalcogenides via first-principles simulations. By using accurate hybrid functional and quasiparticle methods, we show the single-layer group IV-V and group V-IV-III-VI are indirect bandgap semiconductors with their bandgaps and band edge positions conforming to the criteria of photocatalysts for water splitting. By applying a biaxial strain on single-layer group IV-V, single-layer group IV nitrides show a potential on mechanical sensors due to their bandgaps showing an almost linear response for strain. Furthermore, our calculations show that both single-layer group IV-V and group V-IV-III-VI have absorption from the visible light region to far-ultraviolet region, especially for single-layer SiN-AlO and SnN-InO, which have strong absorption in the visible light region, resulting in excellent potential for solar energy conversion and visible light photocatalytic water splitting. Our research provides valuable insight for finding more potential functional two-dimensional semiconductors applied in optoelectronics, solar energy conversion, and photocatalytic water splitting.

Figure 1

(a) and (b) Top and side views of the single-layer group IV-V structure, respectively, marked with their structural parameters. The blue and red spheres stand for group IV and group V atoms, respectively. (c) Brillouin zone of the single-layer group IV-V and main high symmetric points. (d) Illustration of photocatalytic water splitting. The band edge positions of a photocatalysts must be aligned with reference to the redox potentials for water splitting.

Figure 2

Phonon band dispersions of single-layer group IV-V ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P) marked with their corresponding substance names, which exhibit outstanding kinetic stability, as shown on the left. For the finite temperature molecular dynamics simulations at 300 K, free energies as functions of time-step at temperature $T=300\mathrm{K}$ and the crystal structures of single-layer GeN and GeP (see insets) corresponding to the last free energy maximum in the $T=300\mathrm{K}$ case are shown on the right, which shows that single-layer GeN and GeP are stable at room temperature.

Figure 3

(a)–(c) Band structures of single-layer SiN, GeN, and SnN, respectively. (d)–(f) Band structures of single-layer SiP, GeP, and SnP, respectively. The VBM is set to zero by green dash lines.

Figure 4

(a)–(c) TDOS and PDOS of single-layer group IV nitrides ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn), respectively. (d)–(f) TDOS and PDOS of single-layer group IV phosphides ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn).

Figure 5

Band edge positions of single-layer group IV-V ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P) relative to the vacuum level at zero strain calculated with the HSE06 functional. The standard redox potentials for water splitting are shown for comparison.

Figure 6

(a) and (b) The changes of bandgaps for the group IV nitrides and group IV phosphides, respectively, with biaxial strain. (c) and (d) Strain effects on band edge positions of the group IV nitrides and group IV phosphides, respectively.

Figure 7

(a)–(e) The absorption spectra of group IV-V except for single-layer SnP. (f) The absorption spectra of SnP. These absorption spectra are calculated by $G_0{W}_0+\mathrm{BSE}$. The black lines stand for their absorption spectra without strain, and the red lines stand for their absorption spectra with ultimate biaxial tensile strain as photocatalysts for water splitting.

Figure 8

(a) and (b) Top and side views of the group V-IV-III-VI ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P; $\mathrm{III}=\mathrm{Al},\mathrm{Ga}$, Ga, and In; $\mathrm{VI}=\mathrm{O}$ and S), respectively. The blue, red, green, and pink spheres stand for group IV, group V, group III, and group VI atoms, respectively.

Figure 9

Phonon band dispersions of single-layer group V-IV-III-VI ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P; $\mathrm{III}=\mathrm{Al},\mathrm{Ga}$, and In; $\mathrm{VI}=\mathrm{O}$ and S) marked with their corresponding substance names, which exhibit outstanding kinetic stability, as shown in the left. For the finite temperature molecular dynamics simulations at 300 K, free energies as functions of time-step at temperature $T=300\mathrm{K}$ and the crystal structures of single-layer GeN-Gao and GeP-GaS (see insets) corresponding to the last free energy maximum in the $T=300\mathrm{K}$ case are shown on the right, which shows that single-layer GeN-GaO and GeP-GaS are stable at room temperature.

Figure 10

Band structures of single-layer group V-IV-III-VI calculated with the HSE06 functional. (a)–(c) Band structures of single-layer SiN-AlO, GeN-GaO, and SnN-InO, respectively. (d)–(f) Band structures of single-layer SiP-AlS, GeP-GaS, and SnP-InS, respectively. The VBM is set to zero by green dash lines.

Figure 11

Band edge positions of group V-IV-III-VI ($\mathrm{IV}=\mathrm{Si},\mathrm{Ge}$, and Sn; $\mathrm{V}=\mathrm{N}$ and P; $\mathrm{III}=\mathrm{Al},\mathrm{Ga}$, and In; $\mathrm{VI}=\mathrm{O}$ and S) relative to the vacuum level at zero strain calculated with the HSE06 functional. The standard redox potentials for water splitting are shown for comparison.

Figure 12

(a)–(c) The densities of states (DOS) of single-layer SiN-AlO, GeN-GaO, and SnN-InO, respectively. (d)–(f) The DOS of single-layer SiP-AlS, GeP-GaS, and SnP-InS, respectively. The black and red lines are the PDOS of group V-IV and group III-VI of single-layer group V-IV-III-VI. The TDOS of single-layer group V-IV (green lines) are to compare with the DOS of single-layer group V-IV-III-VI. The red dotted line frames indicate the states that are near the CBM and VBM.

Figure 13

The optical spectrum of single-layer group V-IV (black lines) and single-layer group V-IV-III-VI (red lines) calculated by $G_0{W}_0+\mathrm{BSE}$.