Sang-Do Han

AlGaN/GaN two-dimensional-electron gas heterostructures on 200 mm diameter Si(111)

This Letter reports on the epitaxial growth, characterization, and device characteristics of crack-free AlGaN/GaN heterostructures on a 200 mm diameter Si(111) substrate. The total nitride stack thickness of the sample grown by the metal-organic chemical vapor deposition technique is about 3.3 ± 0.1 μm. The structural and optical properties of these layers are studied by cross-sectional scanning transmission electron microscopy, high-resolution x-ray diffraction, photoluminescence, and micro-Raman spectroscopy techniques. The top AlGaN/GaN heterointerfaces reveal the formation of a two-dimensional electron gas with average Hall mobility values in the range of 1800 to 1900 cm2/Vs across such 200 mm diameter GaN on Si(111) samples. The fabricated 1.5 μm-gate AlGaN/GaN high-electron-mobility transistors exhibited the drain current density of 660 mA/mm and extrinsic transconductance of 210 mS/mm. These experimental results show immense potential of 200-mm diameter GaN-on-silicon technology for electronic devi...

Luminescence optimization with superior asymmetric ratio (red/orange) and color purity of MBO3:Eu3+@SiO2 (M = Y, Gd and Al) nano down-conversion phosphors

Y1−xBO3:Eux3+ (0.07 ≤ x ≤ 0.5 moles) and Y0.7−2x (Gdx, Alx)BO3:Eu3+0.3 (0.05 ≤ x ≤ 0.3 moles) powder phosphors have been synthesized by a novel co-precipitation technique followed by heat treatment. Luminescence optimization was carried out by optimizing the dopant Eu3+ concentration, substitution of Y3+ with Gd3+/Al3+ and finally with SiO2 shell coating. The inversion symmetry of Eu3+ ions were lowered with Eu3+ concentration and substitution of Y3+ with Gd3+/Al3+, respectively. It has been noted that the intensity behavior of PL peaks of Eu3+:5D0 → 7F1, 5D0 → 7F2 are not only sensitive to the inversion symmetry of Eu3+ ions, but also to the monitoring excitation wavelengths. Due to nanosize particle distribution, the optimum activator (Eu3+) concentration (30 mol%) was found to be extremely at higher level, compared to the bulk phosphors. The asymmetric ratio (red/orange) and color purity of the optimized phosphors, Y0.7BO3:Eu0.33+ (with crystallite size, D = 32 nm) and Y0.3Gd0.2Al0.2BO3:Eu3+ (D = 17 nm) were further enhanced with an SiO2 coating. Based on the systematic study, the nanophosphor Y0.7BO3:Eu0.33+@SiO2 with an R/O ratio as 6.710 and color coordinates (x = 0.6612, y = 0.3357) is optimized as a remarkable phosphor having superior features than the commercial, available literature data results.

Citric Acid Assisted Sol-Gel Synthesis and Photoluminescence Characteristics of CaAl1.8Y0.2-xO4:xTb Nanoparticles

In recent years, rare earth ions-activated nanostructure materials have been attracting much interest due to the excellent luminescence and potential applications in luminescent devices and display equipment, such as lighting, field emission display (FED), cathode ray tubes (CRT), and plasma display panels (PDP) resolution[1-6]. In the present time, field emission display (FEDs) , plasma display panels (PDPs) are attracting deal of attention as new display technology . Scientist have undertaken investigations of the influence of particle size on the optical and electronic properties of nanocrystal materials of rare earth oxides [7-8]. The origion of nanoparticle research can be said to be in study of colloids ,their synthesis and characteristics. The quantum confinement and major changes observed in other properties have been the subject of intense research .The surface and interface of nanocrystal play an important role in the optical and electronic properties . Many phosphors have been made in nanophase by employing different techniques .

Sol-gel Combustion Hybrid Method for Nano-oxide Synthesis

Nanopowders were synthesized employing a new route sol-gel combustion hybrid method using acetylene black as a fuel. The dried gels exhibited auto-catalytic combustion behavior. ITO and FTO nanopowders with narrow size distribution were obtained at 750degC. Crystal structures were examined by powder X-ray diffraction (XRD) and particle morphology as well as crystal size was investigated by scanning electron microscopy (SEM). The size of nanopowder was found to be in the range of 16nm to 33 nm.