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Optoelectronic technologies are based on families of semiconductor alloys. It is rare that a new semiconductor alloy family is developed to the point where epitaxial growth is possible; since the 1950s, this has happened approximately once per decade. Herein, this work demonstrates epitaxial thin film growth of semiconducting chalcogenide perovskite alloys in the Ba‐Zr‐S‐Se system by gas‐source molecular beam epitaxy (MBE).  This work stabilizes the full rangey= 0 − 3 of compositions BaZrS_(3‐y)Se_yin the perovskite structure. The resulting films are environmentally stable and the direct band gap (E_g) varies strongly with Se content, as predicted by theory, withE_g= 1.9 − 1.5 eV fory=  0 − 3. This creates possibilities for visible and near‐infrared (VIS–NIR) optoelectronics, solid‐state lighting, and solar cells using chalcogenide perovskites.

 

Perovskite chalcogenides are gaining substantial interest as an emerging class of semiconductors for optoelectronic applications. High-quality samples are of vital importance to examine their inherent physical properties. We report the successful crystal growth of the model system, BaZrS 3 and its Ruddlesden–Popper phase Ba 3 Zr 2 S 7 by a flux method. X-ray diffraction analyses showed the space group of Pnma with lattice constants of a = 7.056(3) Å, b = 9.962(4) Å, and c = 6.996(3) Å for BaZrS 3 and P 4 2 / mnm with a = 7.071(2) Å, b = 7.071(2) Å, and c = 25.418(5) Å for Ba 3 Zr 2 S 7 . Rocking curves with full width at half maximum of 0.011° for BaZrS 3 and 0.027° for Ba 3 Zr 2 S 7 were observed. Pole figure analysis, scanning transmission electron microscopy images, and electron diffraction patterns also establish the high quality of the grown crystals. The octahedral tilting in the corner-sharing octahedral network is analyzed by extracting the torsion angles. 

The making of BaZrS₃thin films by molecular beam epitaxy (MBE) is demonstrated. BaZrS₃forms in the orthorhombic distorted‐perovskite structure with corner‐sharing ZrS₆octahedra. The single‐step MBE process results in films smooth on the atomic scale, with near‐perfect BaZrS₃stoichiometry and an atomically sharp interface with the LaAlO₃substrate. The films grow epitaxially via two competing growth modes: buffered epitaxy, with a self‐assembled interface layer that relieves the epitaxial strain, and direct epitaxy, with rotated‐cube‐on‐cube growth that accommodates the large lattice constant mismatch between the oxide and the sulfide perovskites. This work sets the stage for developing chalcogenide perovskites as a family of semiconductor alloys with properties that can be tuned with strain and composition in high‐quality epitaxial thin films, as has been long‐established for other systems including Si‐Ge, III‐Vs, and II‐VIs. The methods demonstrated here also represent a revival of gas‐source chalcogenide MBE.

 

Among layered and 2D semiconductors, there are many with substantial optical anisotropy within individual layers, including group‐IV monochalcogenidesMX(M = Ge or Sn andX = 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.

 

The synthesis of large‐area TiS₂thin films is reported at temperatures as low as 500 °C using a scalable two‐step method of metal film deposition followed by sulfurization in an H₂S gas furnace. It is demonstrated that the lowest‐achievable sulfurization temperature depends strongly on the oxygen background during sulfurization. This dependence arises because TiO bonds present a substantial kinetic and thermodynamic barrier to TiS₂formation. Lowering the sulfurization temperature is important to make smooth films, and to enable integration of TiS₂and related transition metal dichalcogenides—including metastable phases and alloys—into device technology.