Carrier Lifetime Control of 4H-SiC Epitaxial Layers by Boron Doping

An epitaxial growth technique for 4H-SiC with B doping was developed to control the carrier lifetimes of the epilayers. A linear relationship was observed between the B doping concentration and the flow rate of tri-ethyl-boron, which was used as the B doping source. A room temperature photoluminescence spectrum of a N-and B-doped epilayer showed a broad B-related peak at 2.37 eV instead of a band-edge luminescence, which indicates that the carrier recombination path was changed by the B doping. The minority carrier lifetime decreased (< 30 ns at 250°C) with increasing B doping concentration. The thermal stability of the short carrier lifetime was compared with a conventional carrier lifetime reduction method, namely an electron irradiation technique. After thermal annealing at 1700°C, the carrier lifetime of the electron irradiated epilayer recovered while that of the B-doped epilayer remained, indicating that the carrier lifetime controlled by the B doping technique was more stable against the thermal processes.

Investigations on Structural and Optical Properties of Hydrothermally Synthesized Zn2SnO4 Nanoparticles

Ternary oxide Zn2SnO4 has emerged as a promising material due to its tunable work function, band gap energy, and electric resistivity by simply varying the composition of the material. Zinc stannate nanoparticles were synthesized by green hydrothermal growth technique at 200°C for the reaction time of 24 h using stannic chloride pentahydrate (SnCl4·5H2O) and zinc chloride (ZnCl2) as precursors maintained at pH value of 8. X-ray diffraction analysis confirmed the phase purity and high crystalline nature of the synthesized sample. The estimated crystallite size was about 12.3 nm corresponding to the most prominent plane (311) using Scherrer equation. Morphology of the sample was characterized by SEM analysis, which confirmed the presence of small size nanoparticles. The optical property of synthesized sample was studied by using UV-visible and PL spectroscopy analysis. The derived optical band gap of 3.94 eV was found to be blue shifted as compared to bulk Zn2SnO4 (3.6 eV), which should be attributed to the quantum size effects. Room temperature photoluminescence spectrum showed emission bands at 397 nm and 468 nm.

Effect of Nature of Surfactant on the Formation of β-Ag2Se Nanoparticles and Optical Properties of β-Ag2Se and ZnS/β-Ag2Se Nanocomposite

Surfactant assisted synthetic route was followed to prepare silver selenide (β-Ag2Se) nanoparticles. The effect of three different surfactants viz., Triton X100, SDS and CTAB in the formation of silver selenide nanoparticles had been examined. Pure and crystalline β-Ag2Se nanophase was obtained in the presence of Triton X100 and SDS. However, the presence of CTAB leads to metallic silver formation. Nano Composite of β-Ag2Se and ZnS was fabricated in the presence of glycine as a molecular linker. The products were characterized by different techniques such as XRD, FT-IR, SEM and TEM. Room temperature photoluminescence spectrum of the ZnS/ β-Ag2Se nanocomposite exhibited two emission peaks at around 286 nm and 392 nm with enhanced intensity (lex= 250 nm).

EFFECT OF VANADIUM CONTENT ON PHOTOLUMINESCENCE AND MAGNETIC PROPERTIES OF DOPED ZnO THIN FILMS

ZnO : V thin films with different doping concentration (0%, 1.8%, 3.9%, 6.8%, 10%, and 13%) were fabricated by direct current magnetron sputtering. The X-ray diffraction patterns show that the wurzite structure changed with doping concentration. Furthermore, we could not find any vanadium cluster or phase separation in the X-ray diffraction patterns. The photoluminescence of ZnO : V with different vanadium concentration was investigated. The room temperature photoluminescence spectrum indicates that the films have purple band with 370 nm and the bands with 475 and 490 nm. The peak intensity of room temperature photoluminescence spectrum was affected by vanadium contents and its position remained stable. The intensity of band with 370 nm increases with raising the vanadium concentration and then decreases. The hysteresis behavior indicates that films were ferromagnetic at 50 K. Room temperature ferromagnetism was observed for the film with the doping concentration at 6.8%. However, in this case almost no hysteresis is noticeable. The results implied that the doping concentration and crystalline microstructure influence strongly the film's magnetic characteristics. Increasing the vanadium content in the film caused the degradation of the magnetic ordering.

Synthesis and characterization of zinc sulfide hollow microspheres

The successful synthesis of ZnS hollow microspheres by a solvothermal route is reported. The synthesis was achieved by a proper selection of a sulfur source, i.e., Na2S2O3⋅5H2O or (NH2)2CS, to react with Zn(CH3COO)2⋅2H2O in mixed solvents of ethylene glycol and deionized water. The ZnS products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy. XRD identified the ZnS products to have either zinc blende or wurtzite structure. SEM images revealed hollow ZnS microspheres with 1 to 2 μm diameters and 100 to 200 nm shell thicknesses. TEM images confirmed that the hollow ZnS microspheres were assembled by ZnS crystalline nanocrystallites. The room-temperature photoluminescence spectrum of the zinc blende hollow microspheres showed a strong green emission at 514 nm and weak emission at 379 nm.

Hydrogen-Assisted Synthesis and Optical Properties of Single-Crystalline Cd0.9Mn0.1S Nanobelts

High quality Cd0.9Mn0.1S nanobelts have been synthesized using a one-step thermal evaporation method in large scale. Their morphology and microstructures were determined by X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and photoluminescence spectroscopy. The observations revealed that the as-synthesized Cd0.9Mn0.1S nanobelts were high quality single crystalline with hexagonal wurtzite structure. The nanobelts grew along [0 −1 1 0] direction with side surfaces of ± (0 0 0 1) and top surfaces of ± (2 1 1 0). The nanobelts can range in length from several tens to a hundred microns, in thickness about 50 nm and in tapered width 50 to 300 nm. A hydrogen-assisted vapor-liquid-solid (VLS) combined with vapor-solid (VS) formation mechanism is also proposed to interpret the growth of Cd0.9Mn0.1S nanobelts in our work. The room-temperature photoluminescence spectrum of Cd0.9Mn0.1S nanobelts featured two luminescence peaks around 515 and 596 nm, which could be attributed to surface state emission and Mn2+ ion intra-3d (4T1–6A1) transition, respectively.