TY - JOUR

T1 - Glassy GaS: transparent and unusually rigid thin films for visible to mid-IR memory applications

AU - Tverjanovich, Andrey

AU - Khomenko, Maxim

AU - Bereznev, Sergei

AU - Fontanari, Daniele

AU - Sokolov, Anton

AU - Usuki, Takeshi

AU - Ohara, Koji

AU - Le Coq, David

AU - Masselin, Pascal

AU - Bychkov, Eugene

N1 - Funding Information: This work was supported by the Ministry of Science and Higher Education under agreement 075-15-2019-1950; state assignment FSRC ‘Crystallography and Photonics’ Russian Academy of Sciences. The experiments at SPring-8 were approved by the Japan Synchrotron Radiation Research Institute (proposal No. 2017A1067) and supported by the Centre for Advanced Science and Technology (Japan). The work at Tallinn University of Technology (Estonia) was supported by the European Union through the European Regional Development Fund project ‘Center of Excellence’ TK141. The optical measurements in part were carried out in the resource center of St. Petersburg State University: ‘Center for Optical and Laser Materials Research’. The FPMD simulations were carried out using the HPC computing resources at Lomonosov Moscow State University and at the ILIT RAS in Shatura (Moscow Region). This work was also granted access to the HPC resources of IDRIS (France) under the allocation 2019-A0070910639 made by GENCI (Grand Equi-pement National de Calcul Intensif) and using the CALCULCO computing platform, supported by SCoSI/ULCO (Service COmmun du Système d’Information de l’Universitédu Littoral Côte d’Opale). E. B. is also grateful to Dr F. Sava (National Institute of Materials Physics, Romania) for providing a gallium sulfide film used in preliminary measurements.

PY - 2020/11/28

Y1 - 2020/11/28

N2 - Phase-change materials based on tellurides are widely used for optical storage (DVD and Blu-ray disks), non-volatile random access memories and for development of neuromorphic computing. Narrow-gap tellurides are intrinsically limited in the telecom spectral window, where materials having a wider gap are needed. Here we show that gallium sulfide GaS thin films prepared by pulsed laser deposition reveal good transparency from the visible to the mid-IR spectral range with optical gap Eg = 2.34 eV, high refractive index nR = 2.50 over the 0.8 ≤ λ ≤ 2.5 μm range and, unlike canonical chalcogenide glasses, the absence of photo-structural transformations with a laser-induced peak power density damage threshold above 1.4 TW cm-2 at 780 nm. The origin of the excellent damage threshold under a high-power laser and UV light irradiation resides in the rigid tetrahedral structure of vitreous GaS studied by high-energy X-ray diffraction and Raman spectroscopy and supported by first-principles simulations. The average local coordination number appears to be 〈m〉 = 3.44, well above the optimal connectivity, 2.4 ≤ 〈m〉 ≤ 2.7, and the total volume of microscopic voids and cavities is 34.4%, that is, lower than for the vast majority of binary sulfide glasses. The glass-crystal phase transition in gallium sulfide thin films may be accompanied by a drastic change in the nonlinear optical properties, opening up a new dimension for memory applications in the visible to mid-IR spectral ranges.

AB - Phase-change materials based on tellurides are widely used for optical storage (DVD and Blu-ray disks), non-volatile random access memories and for development of neuromorphic computing. Narrow-gap tellurides are intrinsically limited in the telecom spectral window, where materials having a wider gap are needed. Here we show that gallium sulfide GaS thin films prepared by pulsed laser deposition reveal good transparency from the visible to the mid-IR spectral range with optical gap Eg = 2.34 eV, high refractive index nR = 2.50 over the 0.8 ≤ λ ≤ 2.5 μm range and, unlike canonical chalcogenide glasses, the absence of photo-structural transformations with a laser-induced peak power density damage threshold above 1.4 TW cm-2 at 780 nm. The origin of the excellent damage threshold under a high-power laser and UV light irradiation resides in the rigid tetrahedral structure of vitreous GaS studied by high-energy X-ray diffraction and Raman spectroscopy and supported by first-principles simulations. The average local coordination number appears to be 〈m〉 = 3.44, well above the optimal connectivity, 2.4 ≤ 〈m〉 ≤ 2.7, and the total volume of microscopic voids and cavities is 34.4%, that is, lower than for the vast majority of binary sulfide glasses. The glass-crystal phase transition in gallium sulfide thin films may be accompanied by a drastic change in the nonlinear optical properties, opening up a new dimension for memory applications in the visible to mid-IR spectral ranges.

KW - ABSORPTION

KW - CHALCOGENIDE GLASS

KW - CHEMICAL-VAPOR-DEPOSITION

KW - CRYSTAL-STRUCTURE

KW - DYNAMICS

KW - MOLECULES

KW - NONLINEAR-OPTICAL PROPERTIES

KW - PHASE-CHANGE MATERIALS

KW - STRUCTURAL-ANALYSIS

KW - TEMPERATURE-DEPENDENCE

UR - http://www.scopus.com/inward/record.url?scp=85096352478&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/dcd6e90e-525d-3d39-bd47-7ad68ab2f584/

U2 - 10.1039/D0CP04697C

DO - 10.1039/D0CP04697C

M3 - Article

VL - 22

SP - 25560

EP - 25573

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 44

ER -