[en] In this study, the electrical, optical, and structural properties of tungsten (W)-doped Ge_8Sb_2Te_1_1 thin films were investigated. Previously, GeSbTe alloys were doped with various materials in an attempt to improve the thermal stability. Ge_8Sb_2Te_1_1 and W-doped Ge_8Sb_2Te_1_1 films with a thickness of 200 nm were fabricated by using an RF magnetron reactive co-sputtering system at room temperature on Si (p-type, 100) and glass substrate. The fabricated thin films were annealed in a furnace in the ∼ 0 - 400 ℃ temperature range. The optical properties were analyzed using a UV-Vis-IR spectrophotometer, and by using Beer’s Law equation, the optical-energy band gap (E_o_p), slope B"1"/"2, and slope 1/F were calculated. For the crystalline materials, an increase in the slope B"1"/"2 and 1/F was observed, exhibiting a good effect on the thermal stability in the amorphous state after the phase change. The structural properties were analyzed by X-ray diffraction, and the result showed that the W-doped Ge_8Sb_2Te_1_1 had a face-centered-cubic (fcc) crystalline structure increased crystallization temperature (T_c). An increase in the T_c increased the thermal stability in the amorphous state. The electrical properties were analyzed using a 4-point probe, exhibiting an increase in the sheet resistance (R_s) in the amorphous and the crystalline states indicating a reduced programming current in the memory device.

[en] In this work, we evaluated the structural, electrical and optical properties of carbon-doped Ge8Sb2Te11 thin films. In a previous work, GeSbTe alloys were doped with different materials in an attempt to improve the thermal stability. Ge8Sb2Te11 and carbon-doped Ge8Sb2Te11 films of 250 nm in thickness were deposited on p-type Si (100) and glass substrates by using a RF magnetron reactive co-sputtering system at room temperature. The fabricated films were annealed in a furnance in the 0 ∼ 400 ◦C temperature range. The structural properties were analyzed by using X-ray diffraction (XRD), and the result showed that the carbon-doped Ge8Sb2Te11 had a face-centeredcubic (fcc) crystalline structure and an increased crystallization temperature (Tc). An increase in the Tc leads to thermal stability in the amorphous state. The optical properties were analyzed by using an UV-Vis-IR spectrophotometer, and the result showed an increase in the optical-energy band gap (Eop) in the crystalline materials and an increase in the Eop difference (ΔEop), which is a good effect for reducing the noise in the memory device. The electrical properties were analyzed by using a 4-point probe, which showed an increase in the sheet resistance (Rs) in the amorphous state and the crystalline state, which means a reduced programming current in the memory device.

[en] Highlights: • TeO_2.33/SiO₂ 1D PCs were prepared by using sputtering technique. • Photonic band structures in the PCs with and without a defect layer were analyzed. • Measured transmittance spectra are in good agreement with simulated results. • The defect mode moved towards the longer wavelength after laser exposure. - Abstract: The aim of this work is to experimentally investigate one-dimensional (1D) photonic crystals (PCs) and the photo-induced effect of their defect layer. A radio frequency (RF) magnetron sputtering technique was used to fabricate ten-pair 1D PCs with and without a single defect layer, utilizing TeO_2.33 and SiO₂ with different refractive indices. The photonic band structures in the PCs were also analyzed, and the measured transmittance (T) spectra were compared with the simulated results. The 1D PC without a defect layer had a forbidden band gap in the wavelength range of 1203–1421 nm. The 1D PC with defect layer generated a sharp peak within a photonic band gap (PBG) at the central wavelength of 1291 nm. After exposure to a He-Cd laser of λ = 325 nm, the resonant T peak shows red-shift because of photodarkening effect caused by the behavior of valence-alternation pairs (VAPs) in amorphous chalcogenides.

[en] Arrays of two-dimensional multi-paired photonic crystals (PCs) have been fabricated by a multiple-exposure nanosphere lithography (MENSL) method utilizing a self-assembled nanosphere as a lens mask and an expanded He–Cd laser. The nanospheres were self-assembled on a photoresist. The masked PR was then multi-exposed with changing rotation angle (θ) and tilt angle (γ). Scanning electron microscopy reveals that MENSL is a useful tool for fabricating multi-paired PCs with various lattice structures.