Two-dimensional (2D) indium selenide (InSe) has been widely studied for applications in transistors and photodetectors, benefitting from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and β-phase) of InSe, only the crystal lattice of InSe in β-phase (β-InSe) belongs to a nonsymmetry point group of $D_{6h}^4$, which indicates a stronger anisotropic transport behavior and a potential in the polarized photodetection of β-InSe based optoelectronic devices. Therefore, we prepare the stable p-type 2D layered β-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β-InSe have been experimentally and theoretically proved. It shows that the β-InSe based device has a ratio of 3.76 for the maximum to minimum dark current and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β-InSe as a competitive candidate for filter-free polarization sensitive photodetectors.

In contrast to zero‐bandgap metallic graphene, the binary semiconducting compound, InSe, possesses a tunable bandgap. Herein, a range of particle sizes of β‐InSe from bulk to few‐layer nanosheets and quantum dots are carefully prepared. The size‐dependent bandgap variation and photon‐induced carrier dynamics of InSe are systemically investigated. In contrast to the normal size‐dependent carrier lifetime trend observed at 700 nm, anomalous size‐independent carrier decay is observed at 500 nm. Through time‐dependent density functional theory calculations, the normal carrier lifetimes at lower probe photon energies are attributed to in‐plane excitons, whereas the abnormal size‐independent carrier lifetimes at higher probe photon energies are found to be stimulated by surface‐bound excitons. In view of the robust surface exciton, this suggests that InSe may possess an outstanding optoelectronic performance in the shorter wavelength range. Through photoelectrochemical detection experiments, it is confirmed that InSe features a high photocurrent density and stability and, in particular, a more distinct photoresponse at short wavelengths than at longer ones. Comprehending and quantifying the role of the surface‐bound excitons in InSe across a broad range of semiconductor nanostructures and their fundamental properties may play an important role in understanding the physical properties of 2D III–VI compound materials.

Abstract Unlike traditional two-dimensional layered materials, tellurium (Te) shows its one-dimensional van der Waals structure and triggers intensive researches. Through a density functional theory coupled with the nonequilibrium Green’s function calculation, we found that bilayer tellurene has a broad photoelectric response over the range from the visible to the near-infrared region. Besides, bilayer tellurene photodetector presents an ultra-strong anisotropic photo-responsivity and an ultra-high extinction ratio (~2812 at the photon energy of 3.4 eV) because of its non-layer/chain structure, which is superior to the antimonene (~145) and phosphorene/blue phosphorene bilayers (~240). Time-domain first principle study further reveals that the ultra-strong anisotropy comes from the transition of Te 5p bonding orbitals along or perpendicular to the chain directions. With these excellent optoelectronic merits, bilayer tellurene may become a promising candidate for next-generation photoelectronic devices.

The in-plane anisotropy of monolayer InSe plays a critical role in the application of photodetectors. In this work, through nonequilibrium Green’s function density functional theory (NEGF-DFT) and time-dependent density functional...