Abstract
The 2D semiconductor indium selenide (InSe) has attracted significant interest due its unique electronic band structure, high electron mobility, and wide tunability of its band gap energy achieved by varying the layer thickness. All these features make 2D InSe a potential candidate for advanced electronic and optoelectronic applications. Here, the discovery of new polymorphs of InSe with enhanced electronic properties is reported. Using a global structure search that combines artificial swarm intelligence with first-principles energetic calculations, polymorphs that consist of a centrosymmetric monolayer belonging to the point group D 3d are identified, distinct from well-known polymorphs based on the D 3h monolayers that lack inversion symmetry. The new polymorphs are thermodynamically and kinetically stable, and exhibit a wider optical spectral response and larger electron mobilities compared to the known polymorphs. Opportunities to synthesize these newly discovered polymorphs and viable routes to identify them by X-ray diffraction, Raman spectroscopy, and second harmonic generation experiments are discussed.
Highlights
Introduction and backgroundAtomically thin two-dimensional (2D) layered van der Waals semiconductors with high carrier mobility and tunable band gap energy hold promise for next-generation nanoscale electronics and optoelectronics
Through a global structure search study that combines artificial swarm intelligence with first-principles energetic calculations, we identify a new monolayer polymorph that belongs to the point group D3d with inversion symmetry, distinct from the known non-centrosymmetric D3h monolayer
We explored via swarm-intelligence based computational structure searches the free energy landscape of 2D layered semiconductor indium selenide (InSe) investigate the possibility of new polymorphs
Summary
Thin two-dimensional (2D) layered van der Waals (vdW) semiconductors with high carrier mobility and tunable band gap energy hold promise for next-generation nanoscale electronics and optoelectronics. We report on a new monolayer polymorph of InSe. Through a global structure search study that combines artificial swarm intelligence with first-principles energetic calculations, we identify a new monolayer polymorph that belongs to the point group D3d with inversion symmetry, distinct from the known non-centrosymmetric D3h monolayer. Through a global structure search study that combines artificial swarm intelligence with first-principles energetic calculations, we identify a new monolayer polymorph that belongs to the point group D3d with inversion symmetry, distinct from the known non-centrosymmetric D3h monolayer It is thermodynamically comparable in energy with the D3h , showing robust phonon and thermal stability, as well as kinetic stability with respect to a transformation to D3h. Three bulk phases based on different stacks of the D3d monolayer are predicted, one of which show an enhanced band gap tunability with varying layer thickness and higher electron mobility compared to the other phases. We discuss how the new phases could be identified by X-ray diffraction (XRD), Raman spectroscopy and second harmonic generation (SHG) measurements, opening realistic prospects for the experimental observation and investigation of the predicted polymorphs
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