Papers by Keyword: PL

Abstract: The production of 150 mm-diameter SiC epitaxial wafers is the key to the spread of SiC power devices. We have developed production technology of the epitaxial growth for 4° off Carbon face (C-face) 4H-SiC epitaxial layers on 150 mm diameter substrates. Several growth parameters and hardware were optimized to obtain high uniformity wafers. We have succeeded in fabricating high quality C-face wafers with smooth surface and high uniformity.

Abstract: CuAlO₂ microcrystallites were synthesized by Sol-gel method at 1200°C with Cu (CH₃COO)₂·H₂O, Al (NO₃)₃·9H₂O and ethylene glycol as raw materials. The phase composition,morphology,and optical properties of CuAlO₂ microcrystallites were chatacterized by X-ray diffraction, Scanning electron microscope,Photoluminescence and UV-visible spectroscopy respectively. The results of XRD show that CuAlO₂ with delafossite crystal structure is obtained. The defect emission were observed through PL spectrum test. It can be concluded that Cu-vacancy may be the possible reason of the observed activated p-type conductivity of CuAlO₂. Can be found three characterized peak (λ₁=290nm, λ₂=410nm, λ₃=430 nm) on the spectra.

Abstract: The carbonized silica (SiO₂:C) nanopowders were prepared by chemical modification of fumed silica (aerosil) by phenyltrimethoxysilane followed by thermal annealing at temperature in range of 500-800 °C in nitrogen flow. Their magnetic properties were investigated by electron paramagnetic resonance (EPR) in the temperature range from 4.2 K to 292 K. The initial and annealed SiO₂:C samples revealed carbon (C) related defects. The carbon related radicals (CRR) in annealed SiO₂:C nanopowders with g-factors 2.0042, 2.0039 were attributed to the oxygen (O)-centered CRR and C-centered CRR with a nearby O heteroatom, respectively. The EPR data were compared with infrared (IR) and photoluminescence (PL) data. It was found that the position of the PL band depends on the type of CRR formed after sample annealing. The PL with maximum intensity at 440 nm was found for the sample annealed at 500°C in which O-centered CRR was observed while in the sample annealed at 600°C in which C-centered CRR with a nearby O heteroatom was observed and graphite-like amorphous C clusters were appeared the peak of the PL band was shifted to the 510-520 nm.

Abstract: ZnO thin films with typical c-axis (0 0 2) orientation were successfully deposited on glass substrates by two-step deposition method; mist-atomization and solution-immersion. The samples were annealed at selected temperature range of 350-500 ᵒC. The prepared samples then analyzed by Raman spectroscopy and photoluminescence (PL) spectroscopy. The optical properties of the samples were studied. The results of different annealing temperatures are also compared to investigate the optical and physical properties of each sample. Photoluminescence (PL) spectra showed low intensity in UV emission and high intensity in the visible emission, which indicates a good surface morphology of the ZnO nanorod. The Raman intensity changes in all sample were also tested.

Abstract: The electrical properties of Cadmium Selenium (CdSe) nanoparticles were measured by using I-V characteristic under illumination of light (AM 1.5, 100mWcm^-2) at room temperature. The cadmium chloride (CdCI) as the Cd precursor and selenium (Se) powder as the Se precursor. In this research, the surface profiler was used to know the thickness of CdSe nanoparticles on the glass substrate. The thickness was used to know the energy band gap by using Tauc plot. The optical properties was measured by using Photoluminescence (PL) at room temperature. The energy band gap for 20 min ,30 min ,40 min and 50 min were 4.25 eV, 4.22 eV, 4.09 eV, and 4.21 eV.

Abstract: Transparent thin film of TiO2 is deposited on glass substrate by e-beam evaporation method with the pressure, deposition rate, and substrate temperature of 3.0 x 10-6m.bar, 3 nm/s and 100 0C respectively. The film is annealed at 500 0C for about 1 hour. The structural property of the films has been studied using GIXRD. The optical property of the film has been studied using UV-Visible and Photoluminescence spectroscopy (PL). Photoluminescence spectra shows intense and sharp peak at 440 nm. The dielectric property of the film is studied by measuring capacitance at different frequencies at room temperature. It is observed that the capacitance decreases with increase in frequency but at high frequency, the capacitance becomes constant. GIXRD data indicates the crystalline property of the film.

Abstract: The present paper prepared a structural epitaxial film of gallium nitride multiple-quantum-well (GaN MQW) blue light-emitting diode (LED) on Si (111) substrates with different conduction types using the metal-organic chemical vapor deposition method. The method prevented the interdiffusion of GaN and Si to achieve high-quality film growth by introducing aluminium nitride (AlN)-interposed layer and rich-Gallium GaN layer with low V/III ratio double buffer layers. Surface analysis shows that the GaN LED epitaxial film on the Si (111) substrate with different conduction types presented an entirely different appearance. The surface roughness of all the samples was less than 3 nm. A much smoother surface of the epitaxial film on the N-type substrate had less roughness, whereas a layered stack surface of the epitaxial film on the P-type substrate had larger surface roughness. The full width at half maximum of the XRD Omega rocking curve with (002) and (102) planes of GaN film grown on the N-type substrate was less than that of the GaN film on the P-type substrate. Furthermore, the film was superior to the samples on the P-type substrate in terms of crystal quality. There was little difference in the peak position of the PL of the epitaxial film on the N-type substrate, but the peak position of the PL of the epitaxial film on the P-type substrate was long and had a large half-peak width. The tensile stress of the GaN film on the P-type substrate was higher. The above results show that the N-type Si (111) substrate with high resistivity is more suitable for the growth of GaN MQW LED epitaxial film.

Abstract: Flower-like ZnO was prepared by using ZnCl₂ and NH₃·H₂O as starting materials employing a simple microwave synthesis method. The result shows that flower-like ZnO microcrystal is obtained with 15mL NH₃·H₂O dropped into ZnCl₂ solution and microwave power of 240W for 20 mins simultaneously. Microstructure and surface morphology were investigated in detail by XRD, SEM. The XRD pattern shows, as-prepared ZnO particles are highly crystallized with a wurtzite structure, SEM result demonstrates that flower structure is closely composed of petaloid unit and consists of a series of the bottom thick and top thin nanorods. By researching on PL properties of ZnO, PL spectra shows it has three emission peaks. Then approximate analysis of the causes of every emission peak was made. A simple analysis of growth mechanism was also made in theory finally.

Abstract: In this article gallium nitride (GaN) nanostructures have been grown through chemical vapor deposition (CVD) on Silicon substrate, no metal catalyst was used. A high purity of gallium nitride powder was evaporated at 1150°C for 3 hour and then annealed at temperature 1000°C under flow of ammonia (NH₃)gas. XRD shows the diffraction peaks located at 2θ= 32.4, 34.4, 36.8, 48.1, 57.8, 63.5, 68.3, 69.2° corresponding to the (100), (002), (101), (102), (110), (103), (200) and (112) diffraction planes of the product. These results revealed that the diffraction peaks can be attributed to the hexagonal GaN phase with lattice constant of a = 3.189 Å and c = 5.200 Å. Raman scattering spectrum shows four phonons mode correspond to GaN nanostructure are detected at 560, 570, 720 and 740 cm^-1 corresponding E₁(TO), E₂(high),A₁(LO) and E₁(LO) respectively. Photoluminescence (PL) of the GaN nanostructure exhibited two emission peaks, a weak and broad ultraviolet (UV) light emission peak at 390 nm and a strong yellow light (YL) emission peak at 550 nm.

Abstract: ZnO nanorods were prepared by immersion method deposited onto Silicon (Si) and gold-seeded Si (Au/Si) substrate. The annealing temperatures were varied from 400, 500 and 600 °C. The effect of annealing temperature on the surface morphology and photoluminescence characteristics was investigated. The samples were characterized by Field Emission Scanning Electron Microscope (FESEM) to study their morphology and structural properties while the optical properties were characterized at room temperature using Photoluminescence Spectroscope. The shape of ZnO showed growth of nanorods with hexagonal shape. As the annealing temperature increased, the morphology study indicates that particle size of ZnO decreased while the crystallinity increases. The structures has high surface area, is a potential metal oxide nanostructures to be develop for optoelectronic devices and chemical sensors.