In-plane anisotropy and short-wave polarized light detection of two-dimensional GeSe2

As a new type of two-dimensional semiconductor material, black phosphorus has attracted wide attention from researchers due to its unique in-plane anisotropy. Recently, several other in-plane anisotropic two-dimensional materials (such as ReS2, ReSe2; SnS, GeSe, etc.) have also been reported. The unique in-plane anisotropy of such materials distinguishes them from the in-plane isotropic two-dimensional materials such as graphene and MoS2, and exhibits special electrical, optical, mechanical and thermal properties, and has been successfully applied to integrated circuits. In inverters, crystal-based diodes, artificial synapses, and polarized photodetectors. Among them, polarized light detection is considered to be an important research field in recent years due to its important position in communication. At present, polarized light detection based on in-plane anisotropic materials such as black phosphorus, ReS2, GeSe, etc., has excellent performance, but because of the small band gap of the above materials (< 2 eV), it is complicated in performing short-wavelength polarization detection. And expensive optical systems adjust their ideal light probe range to short wavelengths.

[Introduction]

Recently, the researcher Hu Jinsong of the Institute of Chemistry of the Chinese Academy of Sciences and the research group of Professor Zhang Yimin of Peking University have proposed a kind of in-plane anisotropic material with a wide band gap, GeSe2 (2.74 eV). The researchers first studied the energy band structure along the plane of GeSe2 through theoretical calculations. The effective masses of holes in the x and y directions were 0.755 m0 and ?1.562 m0, respectively, which theoretically confirmed its in-plane. Anisotropy. Then, through the angular-resolved Raman spectroscopy and the angular-resolved conductance test, the significant in-plane vibration and conductance anisotropy are shown. Subsequently, a photodetector was constructed based on a single GeSe2 nanosheet. It exhibits significant photocurrent difference under the illumination of 450 nm polarized light in different directions, which shows the excellent polarization detection performance of the material in the short-wave region. Finally, the experimental and DFT theoretical calculations show that GeSe2 has a higher adsorption oxygen activation energy (2.12 eV; much higher than 0.71 eV of black phosphorus), thus showing excellent air stability. The research results were published in the Journal of the American Chemical Society under the heading "Air-Stable In-Plane Anisotropic GeSe2 for Highly Polarization-Sensitive Photodetection in Short Wave Region". Ph.D. students Yang Yusi and Liu Shunchang are co-first authors, and Xue Dingjiang, associate researcher, is the co-author. The work was immediately followed by the Journal of Physical Chemistry, and the topic of "Two-dimensional GeSe2 In-plane Anisotropy and Short-wave Polarized Light Detection" was featured in the journal "Acta Phys." –Chim Sin., 2018, DOI: 10.3866/PKU.WHXB201803142).

Figure 1 Gee2 nanosheet material characterization

(a) AFM image of tape stripped GeSe2 sheet

(b) Raman spectroscopy of GeSe2 nanosheets with different thicknesses

(c) SAED image of GeSe2 nanosheets

(d) HRTEM images of GeSe2 nanosheets

Figure 2 GeSe2 crystal structure anisotropy

(a) GeSe2 crystal structure side view

(b) GeSe2 crystal structure top view

(c) GeSe2 three-dimensional Brillouin zone schematic

(d) GeSe2 band structure diagram

Figure 3 GeSe2 vibration and conductance anisotropy

(a) Optical photo of the GeSe2 angular resolution conductance test device

(b) GeSe2 angular resolved Raman spectroscopy

(c) Polar plot of the angular resolution Raman intensity of GeSe2

(d) Polar map of angularly resolved normalized conductance

Figure 4 GeSe2 optical anisotropy and polarization performance characterization

(a) Absorption spectra of GeSe2 nanosheets

(b) Forbidden band width fitting curve of GeSe2 nanosheets

(c) Theoretical absorption spectra in the x and y directions of the GeSe2 layer

(d) GeSe2 angular resolution absorption spectroscopy

(e) Schematic diagram of GeSe2 photodetector

(f) Polar plots of angular resolution normalized photocurrents in linearly polarized light in different directions

Figure 5 GeSe2 stability characterization

(a) AFM image of the newly stripped GeSe2

(b) AFM image of GeSe2 after 30 days in the air

(c) Raman surface scan image of newly stripped GeSe2

(d) Raman surface scan image of GeSe2 after being placed in the air for 30 days

(e) Physical and chemical adsorption processes of oxygen molecules on black phosphorus

(f) Physical and chemical adsorption processes of oxygen molecules on GeSe2

【summary】

In this paper, an in-plane anisotropic material with a wide band gap, GeSe2 (2.74 eV), is proposed. The in-plane structure, vibration, electrical and optical anisotropy properties of the material are studied by theoretical calculations and experimental systems. Based on its optical absorption anisotropy, a novel GeSe2 polarized photodetector was constructed, and its application in short-wavelength polarization detection was reported for the first time. Due to good performance and air stability, GeSe2 polarized light detectors show good application prospects.