Impacts of Si-doping on vacancy complex formation and their influences on deep ultraviolet luminescence dynamics in Al x Ga1-x N films and multiple quantum wells grown by metalorganic vapor phase epitaxy

To give a clue for increasing emission efficiencies of Al x Ga1-x N-based deep ultraviolet light emitters, the origins and influences on carrier concentration and minority carrier lifetime (τminority), which determines the internal quantum efficiency, of midgap recombination centers in c-plane Si-doped Al0.60Ga0.40N epilayers and Al0.68Ga0.32N quantum wells (QWs) grown by metalorganic vapor phase epitaxy were studied by temporally and spatially resolved luminescence measurements, making a correlation with the results of positron annihilation measurement. For the Al0.60Ga0.40N epilayers, τminority decreased as the concentration of cation vacancies (VIII) increased, indicating that VIII, most probably decorated with nitrogen vacancies (VN), VIII(VN) n , are major nonradiative recombination centers (NRCs). For heavily Si-doped Al0.60Ga0.40N, a generation of electron-compensating complexes (VIII-SiIII) is suggested. For lightly Si-doping regime, τminority of the QW emission was increased by appropriate Si-doping in the wells, which simultaneously increased the terrace width. The importance of wetting conditions is suggested for decreasing the NRC concentration.

Synthesis of Highly Active Si-doped TiO2 Nanotube/SnS Hybrids for Photocatalytic Degradation of Toxic Dyes

Heterostructures with nanoscale sizes have great superiorities in photocatalytic environment decontaminant because of their efficient interface charge transfer and great surface area. This work reports the facile fabrication of nano-tubular TiO2 and Si-doped TiO2 (NTs) hybridizing SnS nanocrystallites and their high-efficient photocatalytic activity. The fabricated nanostructures show wide light absorption in the UV-visible region. The SBET, light absorption, hydrophilicity, and photo-induced super hydrophilicity were enhanced by Si-doping and SnS modification. Moreover, high-efficient interface charge transfer was produced after the SnS modification and further enhanced by the Si doping because of band structure modulation. Thus, the Si-doped TiO2 nanotubes/SnS heterostructures showed a remarkably enhanced photocatalytic and Fenton-like photocatalytic activities in dye wastewater treatment than the TiO2 NTs. This work suggests potential materials and their facile fabrication process for the photocatalytic application of environmental decontamination.

Thermal Stability of Silicon-Doped Tetrahedral Amorphous Diamond-Like Carbon Coatings And Improvement of Tribological Properties Through High- Temperature Annealing

We report the structure, mechanical properties, thermal stability, and durability of Si-doped tetrahedral amorphous carbon (Si-ta-C) coatings fabricated using simultaneous filtered cathodic vacuum arc deposition and direct current unbalanced magnetron sputtering. Si doping of 1.25–6.04 at.% was achieved by increasing the unbalanced magnetron sputtering power from 25 to 175 W. Si doping provided functionality to the coating, such as heat resistance, while retaining the high hardness of ta-C coatings. The Si-ta-C coatings were stable up to 600 °C regardless of the Si content, while the coating containing 3.85 at.% Si was stable up to 700 °C. The friction behavior and mechanical properties were dependent on the coating film before and after annealing at 100–200 °C; however, annealing at 300–400 °C decreased disk wear and increased counterpart wear due to an increase in film hardness on account of an endothermic reaction that increased the number of Si–C bonds. This indicates that the basic hardness characteristics of the ta-C coating and the high-temperature structural change of the Si-ta-C coating are important for ensuring high-temperature durability. These characteristics were verified through the low coefficient of friction and wear rate of the 1.25 at.% Si-ta-C coating after annealing at 500 °C.

Improved Performance of GaN-Based Ultraviolet LEDs with the Stair-like Si-Doping n-GaN Structure

A method to improve the performance of ultraviolet light-emitting diodes (UV-LEDs) with stair-like Si-doping GaN layer is investigated. The high-resolution X-ray diffraction shows that the UV-LED with stair-like Si-doping GaN layer possesses better quality and a lower dislocation density. In addition, the experimental results demonstrate that light output power and wall plug efficiency of UV-LED with stair-like Si-doping GaN are significantly improved. Through the analysis of the experimental and simulation results, we can infer that there are two reasons for the improvement of photoelectric characteristics: reduction of dislocation density and alleviating of current crowding of UV-LEDs by introduced stair-like Si-doping GaN.