Photonic Platforms Using In‐Plane Optical Anisotropy of Tin (II) Selenide and Black Phosphorus

Abstract

Among layered and 2D semiconductors, there are many with substantial optical anisotropy within individual layers, including group‐IV monochalcogenides MX (M = Ge or Sn and X = S or Se) and black phosphorous (bP). Recent work has suggested that the in‐plane crystal orientation in such materials can be switched (e.g., rotated through 90°) through an ultrafast, displacive (i.e., nondiffusive), nonthermal, and lower‐power mechanism by strong electric fields, due to in‐plane dielectric anisotropy. In theory, this represents a new mechanism for light‐controlling‐light in photonic integrated circuits (PICs). Herein, numerical device modeling is used to study device concepts based on switching the crystal orientation of SnSe and bP in PICs. Ring resonators and 1 × 2 switches with resonant conditions that change with the in‐plane crystal orientations SnSe and bP are simulated. The results are broadly applicable to 2D materials with ferroelectric and ferroelastic crystal structures including SnO, GeS, and GeSe.

Measuring and Then Eliminating Twin Domains in SnSe Thin Films Using Fast Optical Metrology and Molecular Beam Epitaxy

“…It enables characterization of domain boundaries that are generally challenging to detect. The method can be applied to thin films of other optical anisotropic compounds, like SnS, black phosphorus, and WTe 2 (Supporting Information).…”

“…The surface-air reflectivity at normal incidence on the basal plane depends on crystal orientation, due to the in-plane optical anisotropy (Supporting Information). 15 The difference between refractive index in the zigzag and armchair directions causes a rotation in the reflected light polarization. This rotation is wavelength dependent and is amplified when the incident polarization is aligned at 45°to the optical axes.…”

“…The semiconductor tin selenide (SnSe) is a member of the family of metal monochalcogenides, materials that exhibit phase-change behavior, ferroelasticity, thermo-, piezo-, and ferroelectricity, nontrivial electronic topology, and record-breaking thermoelectric performance. − The layered crystal structure of orthorhombic α-SnSe features an in-plane ferroelastic distortion (Figure a,b) that results in significant anisotropy of tensor quantities, including optical refractive index (SnSe is optically triaxial), and thermal and electrical conductivity. − The large in-plane anisotropy is the basis for proposed functionality including ultrafast, nonthermal, low-loss opto-mechanical domain switching and integrated photonic optical phase shifters based on domain reorientation. − …”

Recent Advances in 2D Material Theory, Synthesis, Properties, and Applications

“…The in-plane ferroelastic distortion of single-crystal thin films can be used for “domain change” applications, whereby the armchair and zigzag directions are switched (exchange of short- and long-bonds within the plane) on a picosecond time scale by pulsed light, leveraging the dielectric anisotropy to realize a diffusionless, martensitic, nonthermal, nonresonant switching process . Such “domain change” functionality could be useful for low-injection-loss optical phase control in photonic integrated circuits . Ferroelectric monolayer and AA-stacked multilayer crystals could be used for electro-optic phase modulation, nonlinear optics, and concepts in ferroelectric nonvolatile memory .…”

“…142 Such "domain change" functionality could be useful for low-injection-loss optical phase control in photonic integrated circuits. 143 Ferroelectric monolayer and AA-stacked multilayer crystals could be used for electro-optic phase modulation, nonlinear optics, and concepts in ferroelectric nonvolatile memory. 144 The topological crystalline insulator phases could enable high-responsivity infrared optical detectors.…”