Two-dimensional $n$-InSe/$p$-GeSe(SnS) van der Waals heterojunctions: High carrier mobility and broadband performance

Recently, constructing van der Waals (vdW) heterojunctions by stacking different two-dimensional (2D) materials has been considered to be effective strategy to obtain the desired properties. Here, through first-principles calculations, we find theoretically that the 2D $n$-InSe/$p$-GeSe(SnS) vdW heterojunctions are the direct-band-gap semiconductor with typical type-II band alignment, facilitating the effective separation of photogenerated electron and hole pairs. Moreover, they possess the high optical absorption strength ($\sim {10}^5$), broad spectrum width, and excellent carrier mobility ($\sim {10}^3\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$). Interestingly, under the influences of the interlayer coupling and external electric field, the characteristics of type-II band alignment is robust, while the band-gap values and band offset are tunable. These results indicate that 2D $n$-InSe/$p$-GeSe(SnS) heterojunctions possess excellent optoelectronic and transport properties, and thus can become good candidates for next-generation optoelectronic nanodevices.

Figure 1

Top view of monolayer (a) InSe, (b) GeSe, and (c) SnS; and side view of (d) InSe/GeSe and (e) InSe/SnS heterojunctions. The 3 × 1 × 1 InSe, 5 × 1 × 1 GeSe, and 5 × 1 × 1 SnS supercells are represented by the rectangle frame. The respective Brillouin zone and the corresponding high-symmetry points Γ, $X$, $Y$, and $T$ are given in (f).

Figure 2

The binding energy as a function of the interlayer distance $d$ in the InSe/GeSe and InSe/SnS heterojunctions.

Figure 3

The band structures of (a) InSe, GeSe, SnS monolayers and (b) InSe/GeSe and (c) InSe/SnS heterojunctions calculated using HSE06 method. The insets of (b) and (c) represent the band-decomposed charge density of the VBM and CBM for the corresponding heterojunctions.

Figure 4

(a), (b) Projected band structures and (c), (d) projected DOS of InSe/GeSe and InSe/SnS heterojunctions calculated using HSE06 method.

Figure 5

Schematic representation of the band alignment including both valence band offset ${\mathrm{\Delta }}_{Ev}$ and conduction band offset ${\mathrm{\Delta }}_{Ec}$ for the (a) InSe/GeSe and (b) InSe/SnS heterojunctions. The optical absorption coefficient α of the (c) InSe/GeSe and (d) InSe/SnS heterojunctions.

Figure 6

The electrostatic potential of (a) GeSe, (b) SnS, and (c) InSe monolayers and (d) InSe/GeSe, (e) InSe/SnS heterojunctions. (f) The transfer directions of electrons and the movement of the Fermi level in the process of forming heterojunctions.

Figure 7

The (a) charge transfer and (b) band gap as a function of the interlayer distance $d$ in the InSe/GeSe and InSe/SnS heterojunctions.

Figure 8

The band gap, band edge, and band offset as a function of the external $E$-field strength in the (a) InSe/GeSe and (b) InSe/SnS heterojunctions.