A method for fabricating Ag coated beam splitter is reported. This is showing specific patterned transmittance by
immersing glass substrates in the mixture of H2SO4 and H2O2 to make negatively charged oxygen sites at silica surface
and then in ethanolic solutions of AgNO3 and butylamine. We controlled the soaking time and molar ratios of the
mixture of AgNO3 and butylamine to pattern % transmittance of electroless coated glass surface. Finally, we made a
functionalized beam splitters showing step function like transmittance and applied this to make multiple laser beams for
display and laser machining.
Photonic device structures often require nano scale lithography techniques for their device fabrication. The techniques
are electron beam lithography and FIB(focused ion beam) pattering. Focused ion beam etching has been used as a
nanolithography tool for the creation of these nanostructures without mask. We obtain nano scale mesa patterns on
InGaN/GaN LED(light emitting diodes) wafer using focused ion beam and characterized. The InGaN/GaN LED wafer
was grown by molecular organic vapor deposition (MOCVD). To reduce the surface damage during FIB patterning, we
used a dielectric mask layer and wet etching to eliminate re-deposition of sputtering materials and Ga+ ion implantations
and ion damage layer during FIB patterning, and finally, removed SiO2 with wet etching. A metal thin layer was
deposited by an ion beam sputter to avoid charging effects during FIB patterning. We obtain a 2-Dimensional patterning
for the fabrication of the high brightness LEDs. This FIB pattering technique can be applied to nanofabrication
optoelectronic devices.
We present a converged spectroscopic system design for performing photoreflectance (PR), electroreflectance (ER), electroluminescence (EL), photoluminescence (PL) and photovoltage (PV) measurements of semiconductors. The design of the experimental setup is described in detail. To test the performance of the system, measurements of a series of InxGa1-xN/GaN light emitting semiconductor with different indium composition of InGaN layer are carried out by use of this system. The experimental reflection and luminescence spectra are analyzed and discussed. The experimental results demonstrate the performance of this system. Optical and electrical properties of In0.15Ga0.85N/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with different quantum well (QW) thicknesses were investigated by electric-field dependent ER spectroscopy. From the ER measurements, we have observed the well-resolved transition peaks related to InGaN QW. Furthermore, the
transitions related to yellow luminescence (YL) from Si-doped GaN and blue luminescence (BL) from Mg-doped GaN were observed in the ER spectra of In0.15Ga0.85N/GaN MQW LEDs. With increasing QW thickness, the additional transitions related to InGaN QW can be attributed to the recombination of excitons localized at the shallow potential states in InGaN QW, originating from the In-poor InGaN regions caused by indium phase
separation in InGaN QW. By applying a reverse bias voltage, the ER features related to InGaN QW were shifted
to higher energy, resulting from the reduction of quantum confined Stark effect in InGaN QW with increasing reverse bias voltage. On the other hand, the ER features from YL and BL band related to the deep and the shallow impurity state exhibit redshift and broaden with reverse bias voltage. These results can be attributed to the reduction of Coulomb interaction between donor and acceptor caused by the increase of depletion regions with increasing reverse bias voltage.
We report new type of micro-EL instrument and its applications for light emitting devices. Our new micro-EL, so-called confocal scanning electroluminescence sprctro-microscope (CSESM) has not only fast image acquisition time but also high image resolution. The newly developed CSESM is combined with confocal laser scanning photoluminescence micsoscope, i.e. micro-PL. Therefore, micro-EL distribution can be directly matched with micro-PL and mechanical chip structure of LED. It is fruitful for providing a fast and non-destructive method to analyze the homogeneity of LEDs in its completely proceeded form. Using this apparatus, we study local intensity and wavelength distribution of electroluminescence for InGaN/GaN blue LED chip. Our results represent that local fluctuations of electroluminescence intensity and wavelength position are closely connected with the fluctuation of local current density, i.e. current spreading features on LED chips.
We have improved charge character on the surface of phosphor particles by dispersed sub micro miter size sulfonate
polystryrene beads and polyelectrolyte dispersant. The surface of TAG phosphor was analyzed with SIMS-TOF. Many
hydrocarbon molecules were existed on the TAG phosphor. We could exchange the hydrocarbon into polyelectrolyte and
sulfonated polystyrene beads. Characterization of the chemical bonging of polystyrene beads adhered on the surface of
the TAG phosphor was archieved with x-ray photoemission spectroscopy (XPS) and FT-Raman. We could measure light
efficiency of the white LED with integrating sphere spectrophotometer. Adhering sub micro miter size sulfonated
polystyrene beads on the surface of TAG phosphor has enhanced extraction efficiency of light from phosphor. The
sulfonated ligand and reduced difference of refractive index between phosphor and encapsulant material are responsible
for the enhancement of extraction efficiency light from phosphor. Additional increase of light extraction has been
observed when the phosphor particles were coated only on and near the LED chip. Surface modified phosphor particle
and phosphor layer have improved LED light efficiency about ten percents.
Excitonic carrier dynamics taking place in InxGa1-xN/GaN multi-quantum-well systems have been studied by low temperature picosecond time resolved photoluminescence (LT-TRPL), HR-TEM, XPS, Dynamic TOF-SIMS, and quantum mechanical simulation methods. Both time-integrated and time-resolved photoluminescence spectra of InxGa1-xN/GaN multi-quantum-wells with different well thickness and Indium composition were measured at 10 K. We assigned the natural radiative lifetime of each sample from the time resolved PL. We observed that the natural radiative lifetime of In InxGa1-xN/GaN multi-quantum-wells depends strongly on the well thickness and Indium composition. To support the measured natural radiative lifetimes, excitonic oscillator strengths of the InxGa1-xN/GaN multi-quantumwells were calculated by using a 2-D particle-in-a-box model as functions of well thickness and Indium composition. Values of the well thickness and Indium compositions from the HR-TEM and XPS compositional depth profiling were used to achieve more realistic computational results and to corroborate the measured natural radiative lifetimes of InxGa1-xN/GaN multi-quantum wells.
The dynamics of the bound and free excitons and exiton polaritons of the ZnO nanorods have been investigated by time resolved photoluminescence in the temperature range from 10 K to 300 K. The samples have been fabricated by catalyst-free metal organic chemical vapor deposition (MOCVD), and have a diameter 35 nm and lengths in the range of 150 nm to 1.1 μm. In the temperature range of 10 K to 50 K, the photoluminescence lifetime of the bound exciton increases as the temperature increases. Photoluminescence lifetime of the free excitons, however, decreases with the temperature. The low temperature (10 K) time resolved photoluminescence spectra reconstructed from the time profiles measured at different frequencies clearly show that the bound exciton decay faster than the free A exciton. This result may be due to the transition from the bound exciton to free exciton because of the local temperature increase. Free B exciton is dominant above 50 K, and forms exciton polariton at high temperatures. At low temperature, photoluminescence lifetimes of the free A and B excitons do not show a clear correlation with the length of the nanorods. At room temperature, however, the photoluminescence lifetime increases monotonically as the length of the nanorods increase in the range of 150 nm to 600 nm. Decrease of the radiative decay rate of the exciton polariton has been invoked to account for the results.
We report on photoluminescence (PL) properties of ZnO epitaxial films and single-crystal nanorods grown by low pressure metalorganic vapor phase epitaxy. Time-integrated PL spectra of the films at 10 K clearly exhibited free A and B excitons at 3.376 and 3.382 eV and bound exciton peaks at 3.360, 3.364, and 3.367 eV. With increasing temperature, intensities of the bound exciton peaks drastically decreased and a free exciton peak was dominant above 40 K. Similarly, vertically well-aligned ZnO nanorod arrays also exhibited free exciton peaks at 3.374 and 3.381 eV, which indicates that ZnO nanorods prepared by the catalyst-fee method are of high optical quality. Furthermore, time-resolved PL measurements at a free exciton peak were carried out at room temperature. The decay profiles were of double-exponential form, and the decay time constants of 180 ps and 1.0 ns were obtained using a least-square fit of the data. Excitation power-dependent PL of ZnO epilayers is also discussed.
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