Layer-dependent switching and photodetection in two-dimensional $\mathrm{In}\mathrm{Se}$ transistors

The two-dimensional layered material-based multifunctional transistors are expected to be core devices in the post-Moore era. However, the relationship between layer thickness and device performance remains unclear. Here, we design the layer $\mathrm{In}\mathrm{Se}$ transistors integrating switching and photodetection functions, exhibiting the fast-switching time and high responsivity when choosing the layer numbers of 2 and 3. Additionally, the maximum photoresponsivity and external quantum efficiency reach up to 0.29 A/W and 136.4% at the wavelength of 310 nm, respectively. The layer-number changing also induces 2 orders of magnitude improvement in and delay time. The dependence between layer number and device performance can provide a basis for designing multifunctional devices.

Figure 1

(a) Side and top view of the lattice structure of monolayer $\mathrm{In}\mathrm{Se}$. (b) Band alignments and (c) absorption spectra of $\mathrm{In}\mathrm{Se}$ with different layers. E_c, E_v, E_F, and E_g represent conduction band edge, valence band edge, Fermi level and band gap of multilayer $\mathrm{In}\mathrm{Se}$, respectively. L is the layer number.

Figure 2

(a) Device structure of few layer $\mathrm{In}\mathrm{Se}$ phototransistor, and linearly polarized light irradiate vertically to the y-z plane at a polarization angle of θ. (b) The photocurrent of monolayer $\mathrm{In}\mathrm{Se}$ as functions of the various photon energies under linearly polarized light with polarization angle of θ. The inset shows the functional relationship between the photocurrent and the polarization angle for photon energies of 3.1, 3.6, and 4.2 eV, respectively. (c) The photocurrent of phototransistors with various layers.

Figure 3

Relationship between (a) responsivity versus wavelength and (b) EQE versus incident light wavelength of $\mathrm{In}\mathrm{Se}$ devices with different layer thickness. (c) Responsivity and EQE under standard AM1.5 sunlight radiation for $\mathrm{In}\mathrm{Se}$ with different layers. (d) Density of states of monolayer $\mathrm{In}\mathrm{Se}$.

Figure 4

(a) Device structure of $\mathrm{In}\mathrm{Se}$ FET with single- and double-gate geometry, respectively. (b),(c) Transfer characteristics and (d),(e) g_m and SS of single- and double-gate 5-nm $\mathrm{In}\mathrm{Se}$ FETs. The black dashed line represents the ITRS HP standard.

Figure 5

(a),(b) Transmission spectra for the gate voltage of −1.5 V, the relationships between (c) SS and I_on and I_off, and (d) τ and PDP of the $\mathrm{In}\mathrm{Se}$ devices with different layers. The inset of (a) shows the transmission spectra for the three-, four-, and five-layer device. The gray region indicates the exterior of the bias window. The blue corner represents the perfect performance region in the upper left corner and lower left corner for (c),(d), respectively.

Figure 6

Transmission eigenstates for SG and DG $\mathrm{In}\mathrm{Se}$-based FETs at the on states with layer numbers of one and five, respectively. The color bar indicates the phase of the eigenstate.

Figure 7

Comparison of (a) I_DS (blue bars) and I_ph (red bars) and (b) I_DS, S, EDP, I_ph, R, and EQE of $\mathrm{In}\mathrm{Se}$-based devices with different layers.