Li doped NiO (LixNi1−xO) thin films were epitaxially grown along [111] orientation on c-sapphire by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated using x-ray diffraction, four probe technique, and UV-visible spectra, respectively. The epitaxial growth of [111] Li doped NiO on [0001] sapphire was determined by using high resolution x-ray Φ scan. Effects of the deposition condition and Li doping concentration variations on the electrical and optical properties of Li doped NiO films were also investigated. The analysis of the resistivity data show that doped Li ions occupy the substitutional sites in the films, enhancing the p-type conductivity. The minimum resistivity of 0.15 Ω cm was obtained for Li0.07Ni0.93O film. The activation energy of Li doped NiO films were estimated to be in the range of 0.11–0.14 eV. Based upon these values, a possible electrical transport mechanism is discussed. A p-n heterojunction has also been fabricated for the optimized p-Li doped NiO with n-ZnO. The insertion of i-MgZnO between the p and n layer led to improved current-voltage characteristics due to reduced leakage current. In the diode architecture, a heteroepitaxial relationship of [111]NiO‖[0001]MgZnO‖[0001]ZnO‖[0001]GZO‖[0001]Al2O3 among the layers was obtained. The p-i-n heterojunction showed good rectification behavior with turn on voltage of 2.8 V and breakdown voltage of 8.0 V.

We have made a comparative study of epitaxial growth of VO2 thin films on c-cut (0001) and r-cut (11¯02) sapphire substrates, and the semiconductor to metal transition (SMT) characteristics of these films have been correlated with their structural details. On c-sapphire, VO2 grows epitaxially in (002) orientation. These (002) oriented VO2 films have 60° twin boundaries due to three equivalent in-plane orientations. The epitaxial VO2 films on r-sapphire consisted of two orientations, namely (200) and (2¯11). The coexistence of these two orientations of VO2 has been explained on the basis of similarity of atomic arrangements in (200) and (2¯11) planes. The thermal hysteresis (ΔH), sharpness of the transition (ΔT), and the transition temperature for VO2 films on c-sapphire were found to be 4.8, 8.5, and 72.6 °C, respectively, which were higher than the corresponding values of 3.3, 5.4, and 60.3 °C for films on r-sapphire. The SMT temperature for VO2 films on c-sapphire was close to the bulk value of 68.0 °C. The significant decrease in transition temperature to 60.3 °C for VO2 films on r-sapphire has been attributed to the compressive strain along [002] direction of VO2.

A novel, highly efficient hole injection material based on a conducting polymer polythienothiophene (PTT) doped with poly(perfluoroethylene‐perfluoroethersulfonic acid) (PFFSA) in organic light‐emitting diodes (OLEDs) is demonstrated. Both current–voltage and dark‐injection‐current transient data of hole‐only devices demonstrate high hole‐injection efficiency employing PTT:PFFSA polymers with different organic charge‐transporting materials used in fluorescent and phosphorescent organic light‐emitting diodes. It is further demonstrated that PTT:PFFSA polymer formulations applied as the hole injection layer (HIL) in OLEDs reduce operating voltages and increase brightness significantly. Hole injection from PTT:PFFSA is found to be much more efficient than from typical small molecule HILs such as copper phthalocyanine (CuPc) or polymer HILs such as polyethylene dioxythiophene: polystyrene sulfonate (PEDOT‐PSS). OLED devices employing PTT:PFFSA polymer also demonstrate significantly longer lifetime and more stable operating voltages compared to devices using CuPc.

Articles you may be interested inA microstructural approach toward the effect of thickness on semiconductor-to-metal transition characteristics of VO2 epilayers

Articles you may be interested inOptimization of the semiconductor-metal transition in VO2 epitaxial thin films as a function of oxygen growth pressure Appl. Phys. Lett. 104, 081913 (2014); 10.1063/1.4866806Sharp semiconductor-to-metal transition of VO2 thin films on glass substrates