InSe as a case between 3D and 2D layered crystals for excitons

T V Shubina,O Briot,A V Platonov,A Tiberj,V Yu Davydov,M A Semina,B Gil,M Moret,W Desrat

doi:10.1038/s41467-019-11487-0

Abstract

InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the P-band of the exciton-exciton scattering while the excitation power increases. The strict energy and momentum conservation rules of the P-band are used to reexamine the exciton binding energy. The new value ≥20 meV is markedly higher than the currently accepted one (14 meV), being however well consistent with the robustness of the excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap (~1.36 eV). Our findings supported by theoretical calculations taking into account the anisotropic material parameters question the pure three-dimensional character of the exciton in InSe, assumed up to now. The refined character and parameters of the exciton are of paramount importance for the successful application of InSe in nanophotonics.

Highlights

InSe is a promising material in many aspects where the role of excitons is decisive
The absorption edge of InSe, being close to that in silicon, offers sufficient solar energy conversion[8,9]. Owing to these exceptional properties, InSe is widely considered as a seminal compound for a number of potential applications that are transformative in many fields of modern physics and nanotechnology[10]
Similar studies of mono-chalcogenides are at the very beginning, it is generally accepted that exciton and exciton complexes will determine their use in nanophotonics

Summary

Introduction

InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the Pband of the exciton-exciton scattering while the excitation power increases. The absorption edge of InSe, being close to that in silicon, offers sufficient solar energy conversion[8,9]. Owing to these exceptional properties, InSe is widely considered as a seminal compound for a number of potential applications that are transformative in many fields of modern physics and nanotechnology[10]. The stacking sequence of tetralayers leads to different polytypes (see Supplementary Note 1) Both widely used γ and β polytypes of InSe have direct energy gap[14,15]. The transitions with E⊥c in InSe occur possible through a weak spin–orbit interaction[18,19,20] (see Supplementary Note 2)

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Results

Conclusion