InSe monolayer: synthesis, structure and ultra-high second-harmonic generation

Abstract

III–IV layered materials such as indium selenide have excellent photoelectronic properties. However, synthesis of materials in such group, especially with a controlled thickness down to monolayer, still remains challenging. Herein, we demonstrate the successful synthesis of monolayer InSe by physical vapor deposition (PVD) method. The high quality of the sample was confirmed by complementary characterization techniques such as Raman spectroscopy, atomic force microscopy (AFM) and high resolution annular dark field scanning transmission electron microscopy (ADF-STEM). We found the co-existence of different stacking sequence (β- and γ-InSe) in the same flake with a sharp grain boundary in few-layered InSe. Edge reconstruction is also observed in monolayer InSe, which has a distinct atomic structure from the bulk lattice. Moreover, we discovered that the second-harmonic generation (SHG) signal from monolayer InSe shows large optical second-order susceptibility that is 1–2 orders of magnitude higher than MoS2, and even 3 times of the largest value reported in monolayer GaSe. These results make atom-thin InSe a promising candidate for optoelectronic and photosensitive device applications.

Second-harmonic generation in single-layer monochalcogenides: A response from first-principles real-time simulations

“…2 with: n sub ≈ 1.45 (fused silica 48 ); n GaSe (ω) = n GaSe (2ω) = 2.8, 8 and n InSe (ω) = 2.86 and n InSe (2ω) = 3. 35,13 . We set F = 1, rather than the value of approximately 20 indicated in Ref.…”

“…IV) that many-body effects do not account for the difference between theoretical predictions 18,19 and experimental estimates. 8,13 We turn then the attention to the experimental results and argue that the extremely large SHG coefficient is an artifact of the model assumed to extract the estimate from the experimental data.…”

Realization of Quantum Hall Effect in Chemically Synthesized InSe

“…As exfoliation produces crystalline flakes randomly, the geometry and thickness cannot be controlled well and it is the largest barrier toward the development of practical applications. Although great strides have been made in the synthesis of BP and InSe thin films using chemical vapor deposition (CVD) or other methods, these 2D crystals' electronic properties are lacking compared to their exfoliated counterparts, due to their reactivity with ambient conditions. Thus far, the demonstration of the quantum Hall effect in a synthesized 2D semiconductor is crucially missing and impedes high‐performance application development.…”

Controlling Defects in Continuous 2D GaS Films for High‐Performance Wavelength‐Tunable UV‐Discriminating Photodetectors

“…In addition, due to difficulties in exfoliation and lack of thickness‐controlled synthesis methods, previous reports were unable to study layered‐dependent properties of the 2D layered material, and to our knowledge, characterization or properties of GaS less than 3 layers (3L) are missing. Furthermore, although other members in the group‐III monochalcogenide‐layered materials with similar structures (GaSe, GaTe, InSe) have attracted intense attention as they have demonstrated superior optical properties, including ultra‐high second‐harmonic generation, giant piezo‐phototronic response, polarization‐dependent absorption, etc., properties of GaS with wide potential remain unexplored as a result of unanswered stability issues and unsatisfying samples. Recently, our group has developed a simple and atmospheric pressure chemical vapor deposition (CVD) method for the growth of 2D GaS crystals, which paved way for further study of the material's stability and layer‐dependent properties.…”