The ability to detect linearly polarized light is central to practical applications in polarized optical and optoelectronic fields and has been successfully demonstrated with polarized photodetection of in-plane anisotropic two-dimensional (2D) materials. Here, we report the anisotropic optical characterization of a group IV–V compound-2D germanium arsenic (GeAs) with anisotropic monoclinic structures. High-quality 2D GeAs crystals show the representative angle-resolved Raman property. The in-plane anisotropic optical nature of the GeAs crystal is further investigated by polarization-resolved absorption spectra (400–2000 nm) and polarization-sensitive photodetectors. From the visible to the near-infrared range, 2D GeAs nanoflakes demonstrate the distinct perpendicular optical reversal with a 75–80° angle on both the linear dichroism and polarization-sensitive photodetection. Obvious anisotropic features and the high dichroic ratio of I pmax /I pmin ∼ 1.49 at 520 nm and I pmax /I pmin ∼ 4.4 at 830 nm are achieved by the polarization-sensitive photodetection. The polarization-dependent photocurrent mapping implied that the polarized photocurrent mainly occurred at the Schottky photodiodes between electrode/GeAs interface. These experimental results are consistent with the theoretical calculation of band structure and band realignment. Besides the excellent polarization-sensitive photoresponse properties, GeAs-based photodetectors also exhibit rapid on/off response. These results demonstrate that the 2D GeAs crystals have promising potential for polarization optical applications.

2D elemental layered crystals, such as graphene and black phosphorus (B-P), have received tremendous attentions due to their rich physical and chemical properties. In the applications of nanoelectronic devices, graphene shows super high electronic mobility, but it lacks bandgap which impedes development in logical devices. As an alternative, B-P shows high mobility of up to about 1000 cm 2 V −1 s −1 . However, B-P is very unstable and degrades rapidly in ambient conditions. Orthorhombic arsenic (black arsenic; b-As) is the "cousin" of B-P; theoretical prediction shows that b-As also has excellent physical and chemical properties, but there is almost no experimental report on b-As. Herein, it is reported on the unique transport characteristics and stability of monolayer and few-layer b-As crystals which are exfoliated from the natural mineral. The properties of field-effect transistors (FETs) strongly depend on the thickness of crystals. In the monolayer limit, the performance shows relatively high carrier mobilities and large on/off ratios. Moreover, the b-As crystals exhibit a relatively good ambient stability. The few-layer arsenic based FET still function after exposure to air for about one month. Therefore, b-As is expected to be a promising 2D material candidate in nanoelectronic devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201802581.properties. [9][10][11] It is considered to be a more promising material than graphene in opto/ nanoelectronic devices. [1,5,6,8,9] However, the deterioration of B-P under atmospheric conditions definitely hinders its applications in practical devices. [12,13] To improve its performance, many attempts have been made. Studies have found that alloying of B-P is a good choice, such as the black arsenic-phosphorus alloy shows tunable bandgap, excellent optical properties, and good ambient stability. [14,15] Another way is to find the new alternative materials.B-As (named arsenene), as a cousin of B-P, has the similar structure configuration with B-P, which is expected to have excellent physical and chemical properties. [16][17][18] Just like most TMDCs and B-P, theoretical studies have verified that the band structures of b-As also have layer dependence. [16] Bulk layered b-As is a direct semiconductor with the bandgap of about 0.3 eV, whereas the monolayer b-As is an indirect bandgap semiconductor with the gap value of about 1-1.5 eV. [16][17][18][19][20] This characteristic leads it to a possibility for applications in optoelectronic and logical devices. Moreover, few-layer b-As is predicted to have high carrier mobility (several thousand square centimeters per volt-second). [20,21] These excellent physical properties make it a good candidate for applications in electronic devices. So far, the experimental synthesis of black arsenic crystals still faces great challenges. [22,23] A recent paper reported that black arsenic is metastable and often stabilized by impurities; and it is very difficult to synt...

Photodetectors with high polarization sensitivity are in great demand in advanced optical communication. Here, we demonstrate that photodetectors based on titanium trisulfide (TiS) are extremely sensitive to polarized light (from visible to the infrared), due to its reduced in-plane structural symmetry. By density functional theory calculation, TiS has a direct bandgap of 1.13 eV. The highest photoresponsivity reaches 2500 A W. What is more, in-plane optical selection caused by strong anisotropy leads to the photoresponsivity ratio for different directions of polarization that can reach 4:1. The angle-dependent photocurrents of TiS clearly display strong linear dichroism. Moreover, the Raman peak at 370 cm is also very sensitive to the polarization direction. The theoretical optical absorption of TiS is calculated by using the HSE06 hybrid functional method, in qualitative agreement with the observed experimental photoresponsivity.