Intrinsic evolutions of dielectric function and electronic transition in tungsten doping Ge2Sb2Te5 phase change films discovered by ellipsometry at elevated temperatures

Abstract

Tungsten (W) doping effects on Ge2Sb2Te5 (GSTW) phase change films with different concentrations (3.2, 7.1, and 10.8%) have been investigated by variable-temperature spectroscopic ellipsometry. The dielectric functions from 210 K to 660 K have been evaluated with the aid of Tauc-Lorentz and Drude dispersion models. The analysis of Tauc gap energy (Eg) and partial spectral weight integral reveal the correlation between optical properties and local structural change. The order degree increment and chemical bond change from covalent to resonant should be responsible for band gap narrowing and electronic transition enhancement during the phase change process. It is found that the elevated crystalline temperature for GSTW can be related to improved disorder degree. Furthermore, the shrinkage of Eg for GSTW should be attributed to the enhanced metallicity compared with undoped GST.

Evolutionary Design and Prototyping of Single Crystalline Titanium Nitride Lattice Optics

“…The algorithm terminated and exported the optimized lattice structure when the fitness value was constant for 30 generations . To account for materials properties, we measured the complex dielectric constants of TiN (Figure S1) by ellipsometry and imported the dielectric function into FDTD models. − Then we calculated the electric field components of light transmitted by a single nanohole (in a periodic array) by FDTD simulations and stored the data for OLEA calculations . To expedite the fitness evaluation step, the OLEA calculated the optical profiles by adding the field components contributed by each lattice unit directly …”

“…FDTD calculations based on commercial software (FDTD Solution, Lumerical Inc., Vancouver, Canada) were used to simulate the linear properties (far-field and near-field) of TiN nanoholes. The optical constants of TiN were taken from ellipsometry measurements and imported to the materials database of Lumerical FDTD. A uniform mesh size of 2 nm (6 nm) was imposed on TiN nanoholes in simulations for a single nanohole (33 × 33 lattice structures).…”

Lattice-Resonance Metalenses for Fully Reconfigurable Imaging

“…The optical constants of Ag were obtained from a reported Kramers–Kronig analysis based on absorptivity measurements . The dielectric properties of PMMA and SU-8 photoresist were taken from ellipsometry measurements and imported to the materials database of Lumerical FDTD. In calculations of periodic Ag NP arrays, a mesh-override size of 2 nm was imposed on the single NP, and periodic boundary conditions were used in x – y directions.…”

Flux periodic oscillations and phase-coherent transport in GeTe nanowire-based devices

“…Magnetotransport measurements: The temperature and magnetic field dependent I-V characteristics and dV/dI curves were measured using a standard lock-in technology in a 3 He cryostat with a base temperature of 0.4 K and a magnetic field range from −8 to 8 T. A four-terminal current driven geometry is employed to directly measuring the voltage drop across the inner section of GeTe nanowire between the nearest internal electrodes. The external pair of electrodes was used for current bias.…”

“…In the past decades, GeTe-based alloys are attracting an increasing interest for their applications in optical data storage and phase change memories due to a reversible rapid transformation between amorphous and crystalline phase 1,2 and a large contrast of optical constants and electrical conductivity for the two phases. 3 In addition, GeTe-rich alloys can be used in intermediate temperature thermoelectric applications for converting waste heat to electrical energy because of their high thermoelectric performance, high thermal and mechanical stability. 4,5 Moreover, the GeTe ferroelectric semiconductor exhibits a giant bulk Rashba effect, [6][7][8][9] which is very interesting for applications in spintronic devices.…”