Intense violet–blue emission and paramagnetism of nanocrystalline Gd3+ doped ZnO ceramics

Nanocrystalline Zn1-xGdxO (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were synthesized by ball milling and subsequent solid-state reaction. The transmission electron microscopy (TEM) micrograph of as synthesized samples revealed the formation of crystallites with an average diameter of 60 nm, and the selected area electron diffraction (SAED) pattern confirmed the formation of wurtzite structure. A red shift in the band gap was observed with increasing Gd3+ concentration. The photoluminescence of nanocrystalline Gd3+ doped ZnO exhibited a strong violet–blue emission. Concentration dependence of the emission intensity of Gd3+ in ZnO was studied, and the critical concentration was found to be 4 mol% of Gd3+. The Gd3+ doped ZnO exhibited paramagnetic behavior at room temperature, and the magnetic moment increased with Gd3+ concentration

Effect of grain boundary scattering on carrier mobility and thermoelectric properties of tellurium incorporated copper iodide thin films

Copper iodide (CuI) is a promising p-type transparent semiconductor with many potential applications in range of fields such as transistors, optoelectronics, solar cells, thermal sensors, and energy harvesting. We report compositional, structural, optical, electrical, and thermoelectric properties of optically transparent tellurium (Te) incorporated CuI films, (CuI)1-xTex where x=0–0.09, prepared by ion beam sputtering. The films are composed of γ-CuI with the presence of elemental tellurium clusters in films prepared with high Te concentration sputtering targets. The carrier mobility decreased from 6.9 ± 0.9 cm2V-1s-1 to 0.7 ± 0.1 cm2V-1s-1, and the electrical conductivity from 84.22 ± 8.45 Scm-1 to 3.97 ± 0.40 Scm-1 for the CuI and (CuI)0.91Te0.09 films, respectively, attributed to a transition from polar optical phonon to grain boundary scattering. The change in the mobility-limiting scattering mechanism decreased the power factor from 454 ± 57 μWm-1K-2 for the CuI film to 34 ± 4 μWm-1K-2 for the (CuI)0.91Te0.09 film. Our study shows that modulating the scattering mechanism in transparent thermoelectric materials is a powerful method to tune their thermoelectric properties

Quasilinear Kane conduction band model in nitrogen-doped indium tin oxide

The band nonparabolicity of indium tin oxide (ITO) polycrystalline thin films is investigated with the quasilinear Kane model through Seebeck and Hall effect measurements. We report Kane model nonparabolic band parameters of m0∗=0.21m0 and C=0.52eV-1 for ITO, in good agreement with historical photoemission, optical, and transport measurements. To do this, the ITO films were doped with nitrogen by ion implantation, with fluences ranging from 5×1014Ncm-2 to 5×1015Ncm-2. The presence of the nitrogen in the films was verified with x-ray photoelectron spectroscopy, and their acceptor character studied theoretically by density functional theory. Experimentally, the doped nitrogen formed NO- defects, deep acceptor states that led to a controlled compensation in carrier concentration from 10.1×1020±0.6×1020cm-3 to 2.9×1020±0.2×1020cm-3. Understanding the band nonparabolicity of degenerately doped transparent conducting oxides is essential for their commercial application in solar cells, transparent thermoelectric generators, and transparent thin film transistors. In this work, the Seebeck and Hall effect approach with the quasilinear Kane model for band nonparabolicity is presented as a practical method by which to study the variation in carrier effective mass without reliance on optical measurements

Investigations on structural, magnetic and electronic structure of Gd-doped ZnO nanostructures synthesized using sol-gel technique

[[abstract]]GdxZn1−x O (x = 0, 0.02, 0.04 and 0.06) nanostructures have been synthesized using sol–gel technique and characterized to understand their structural and magnetic properties. X-ray diffraction (XRD) results show that Gd (0, 2, 4 and 6 %)-doped ZnO nanostructures crystallized in the wurtzite structure having space group C3v (P63mc). Photoluminescence and Raman studies of Gd-doped ZnO powder show the formation of singly ionized oxygen vacancies. X-ray absorption spectroscopy reveals that Gd replaces the Zn atoms in the host lattice and maintains the crystal symmetry with slight lattice distortion. Gd L3-edge spectra reveal charge transfer between Zn and Gd dopant ions. O K-edge spectra also depict the charge transfer through the oxygen bridge (Gd–O–Zn). Weak magnetic ordering is observed in all Gd-doped ZnO samples.[[notice]]補正完

Conversion of p–n conduction type by spinodal decomposition in Zn-Sb-Bi phase-change alloys

Phase-change films with multiple resistance levels are promising for increasing the storage density in phase-change memory technology. Diffusion-dominated Zn2Sb3 films undergo transitions across three states, from high through intermediate to low resistance, upon annealing. The properties of the Zn2Sb3 material can be further optimized by doping with Bi. Based on scanning transmission electron microscopy combined with electrical transport measurements, at a particular Bi concentration, the conduction of Zn-Sb-Bi compounds changes from p- to n-type, originating from spinodal decomposition. Simultaneously, the change in the temperature coefficient of resistivity shows a metal-to-insulator transition. Further analysis of microstructure characteristics reveals that the distribution of the Bi-Sb phase may be the origin of the driving force for the p–n conduction and metal-to-insulator transitions and therefore may provide us with another way to improve multilevel data storage. Moreover, the Bi doping promotes the thermoelectric properties of the studied alloys, leading to higher values of the power factor compared to known reported structures. The present study sheds valuable light on the spinodal decomposition process caused by Bi doping, which can also occur in a wide variety of chalcogenide-based phase-change materials. In addition, the study provides a new strategy for realizing novel p–n heterostructures for multilevel data storage and thermoelectric applications