Self-Powered Broadband Photodetector Based on a Monolayer $\mathrm{In}\mathrm{Se}$ p-i-n Homojunction

The two-dimensional homojunction is promising in electronic and optoelectronic applications. However, its performance is restricted by lattice mismatch and the depletion region. Here, we construct a monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction photodetector. It presents high photoelectric conversion with a wide light response in the photon-energy range from 1.4 to 5 eV, which induces a photocurrent density of 13.13 nA ${\mathrm{m}}^{-1}$ and a photoresponsivity of 0.022 A ${\mathrm{W}}^{-1}$. Moreover, the gate voltage improves the photocurrent and photoresponsivity almost fourfold. Additionally, the increasing dielectric constant of the substrate decreases the photocurrent spectral width, and a low doping concentration is suitable for photodetectors due to high mobility. These results indicate that the two-dimensional p-i-n homojunction is promising for future photoelectric devices.

Figure 1

(a) Side and top views of $\mathrm{In}\mathrm{Se}$ monolayer atoms. (b) Elemental projected electronic band structures and projected density of states. Monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction: (c) sketch and (d) local density of states. Magenta and black represent high and low local density of states, respectively.

Figure 2

Photocurrent density as functions of (a) photon energy and (b) θ (ϕ). Red and blue lines represent linearly and circularly polarized light, respectively. (c),(d) R_ph and EQE, and (e),(f) extinction ratio of the monolayer $\mathrm{In}\mathrm{Se}$ p-i-n homojunction.

Figure 3

(a) Gate-dependent and (b) angle-dependent photocurrent-density spectra at different photon energies of the monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction under zero bias. (c) R_ph and EQE, and (d) extinction ratio at different photon energies. (e) Local density of states under a gate voltage of 1 V. (f) Functional relationship between w and gate voltage.

Figure 4

(a),(b) Photocurrent density and (c),(d) R_ph, EQE, and extinction ratio induced by circularly polarized light of the monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction with ${\mathrm{Si}\mathrm{O}}_2$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, and ${\mathrm{Hf}\mathrm{O}}_2$ substrates.

Figure 5

(a) Photocurrent density, (b) R_ph, (c) EQE, and (d) extinction ratio induced by circularly polarized light of the monolayer $\mathrm{In}\mathrm{Se}$-based p-i-n homojunction with different doping densities.

Figure 6

Photoelectric property of the device with different (a) gate voltages, (b) substrates, and (c) p- (n-) type doping densities.