Jin-Woo Ju

Localized surface plasmon enhanced quantum efficiency of InGaN/GaN quantum wells by Ag/SiO 2 nanoparticles

Optical properties of InGaN/GaN multi-quantum-well (MQW) structures with a nanolayer of Ag/SiO2 nanoparticle (NP) on top were studied. Modeling and optical absorption (OA) measurements prove that the NPs form localized surface plasmons (LSP) structure with a broad OA band peaked near 440-460 nm and the fringe electric field extending down to about 10 nm into the GaN layer. The presence of this NP LSP electrical field increases the photoluminescence (PL) intensity of the MQW structure by about 70% and markedly decreases the time-resolved PL (TRPL) relaxation time due to the strong coupling of MQW emission to the LSP mode.

Structural and optical properties of ZnO∕Mg0.1Zn0.9O multiple quantum wells grown on ZnO substrates

ZnO∕Mg0.1Zn0.9O multiquantum-well (MQW) structures were grown on ZnO substrates by molecular beam epitaxy. Abrupt interfaces and well/barrier width in the MQWs were confirmed by x-ray diffraction measurement and transmission electron microscopy. The transition energy of the localized exciton in the ZnO∕Mg0.1Zn0.9O MQWs with well/barrier width of 5∕8nm was found to be about 3.375eV at low temperature, consistent with theoretical calculation. The first subband energies in the conduction and valence band were calculated to be 19.2 and 5.4meV, respectively. The transition energy showed no shift with excitation power, indicating that the polarization-induced electric field is negligible in the ZnO∕Mg0.1Zn0.9O MQW structures.

High-Brightness GaN-Based Light-Emitting Diodes on Si Using Wafer Bonding Technology

GaN-based light-emitting diodes (LEDs) grown on Si(111) substrates were fabricated with a vertical electrode method by using wafer bonding technology. The fabricated vertical LEDs showed a lower operating voltage and larger light output power than conventional LEDs due to enhancement in current spreading and reduction in tensile strain. The light output power of the vertical structured LEDs was 2.6 times higher than that of conventional LEDs, with an operating voltage at 20 mA reduced from 3.5 to 3.2 V.

Enhanced light output of InGaN/GaN blue light emitting diodes with Ag nano-particles embedded in nano-needle layer

2.7 times increase in room temperature photoluminescence (PL) intensity and 3.2 times increase in electroluminescence (EL) intensity were observed in blue multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) as a result of introduction of nano-needle structure embedded with Ag nanoparticles (NPs) into n-GaN film underlying the active MQW region and thick p-GaN contact layer of LEDs. The nano-needle structure was produced by photoelectrochemical etching. Simultaneously a measurable decrease in room temperature decay time from 2.2 ns in control samples to 1.6 ns in PL was observed. The results are explained by strong coupling of recombination in GaN/InGaN MQWs with Ag NPs related localized surface plasmons.

Anisotropy of In incorporation in GaN/InGaN multiquantum wells prepared by epitaxial lateral overgrowth

Microcathodoluminescence (MCL) spectra and monochromatic MCL images were measured for GaN/InGaN multiquantum well (MQW) structures prepared by epitaxial lateral overgrowth (ELOG). The MQW related peak is redshifted from 462 nm in the normally grown ELOG window region to 482 nm in the laterally overgrown ELOG wing region. Correspondingly, the former appears as dark contrast stripes for long wavelength MCL images and as bright stripes for the short wavelength MCL images. The redshift is consistent with a higher indium incorporation efficiency for growth in the [112¯0] direction compared to the [0001] direction.

Metal-organic chemical vapor deposition growth of InGaN/GaN high power green light emitting diode: Effects of InGaN well protection and electron reservoir layer

We investigated the effects of the well protection layer (WPL) and electron reservoir layer (ERL) on the emission properties of InGaN/GaN green multiple quantum wells (MQWs). In order to increase their emission wavelength by preventing the volatile InGaN well, a thin GaN WPL was coated subsequently on each well layer at the same temperature before ramping-up the temperature to grow the GaN barrier. It was found that the WPL directly influenced the indium content and optical properties of the MQW. The indium content was in fact increased, as was evident from the x-ray diffraction and photoluminescence experiments. Then, to explore the possibility of enhancing the quantum efficiency by increasing the electron capture rate, a superlattice ERL composed of ten pairs of InGaN/GaN was embedded between the MQW and n-GaN. The electroluminescence intensity of the green light emitting diode with the ERL was up to three times higher than that of the diode without the ERL. These results imply that the carrier capture ...

Comparison of electrical properties and deep traps in p-AlxGa1−xN grown by molecular beam epitaxy and metal organic chemical vapor deposition

The electrical properties, admittance spectra, microcathodoluminescence, and deep trap spectra of p-AlGaN films with an Al mole fraction up to 45% grown by both metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were compared. The ionization energy of Mg increases from 0.15 to 0.17 eV in p-GaN to 0.3 eV in 45% Al p-AlGaN. In p-GaN films grown by MBE and MOCVD and in MOCVD grown p-AlGaN, we observed additional acceptors with a concentration an order lower than that of Mg acceptors, with a higher hole capture cross section and an ionization energy close to that of Mg. For some of the MBE grown p-AlGaN, we also detected the presence of additional acceptor centers, but in that case the centers were located near the p-AlGaN layer interface with the semi-insulating AlGaN buffer and showed activation energies considerably lower than those of Mg.

A well protection layer as a novel pathway to increase indium composition : a route towards green emission from a blue InGaN/GaN multiple quantum well

We have investigated the effects of a well protection layer (WPL) on the optical and crystal properties of an InGaN/GaN multiple quantum well (MQW). The five-pair MQW, consisting of an InGaN well grown at 750 °C and a GaN barrier grown at 850 °C, was simply embedded between GaN cladding layers on a sapphire (0001) substrate. While this dual-temperature MQW growth scheme seemed better suited to the GaN barrier quality, it exposed the volatile InGaN well to a higher temperature ambient during the ramping-up process to grow the barrier. In order to prevent damage to the fragile well, a thin GaN WPL was subsequently coated on each well layer at the same temperature before ramping-up the temperature. Consequently, it was found that the WPL directly influenced the indium composition and optical properties of the MQW. The indium composition was in fact increased, as was evident from x-ray diffraction experiments. In addition, photoluminescence measurements showed that the emission peak wavelength was increased from 464 to 520 nm. These results provide evidence that the WPL effectively suppresses indium re-evaporation during the ramping-up time. The present study proposes that the WPL leads to a new way to increase the wavelength of InGaN/GaN MQWs.

High Efficiency InGaN Blue Light-Emitting Diode With

This letter reports high-power and high-efficiency characteristics of the InGaN-based blue light-emitting diode (LED) operating at > 10-W electrical input power in a single-chip package. The LED chip is fabricated as a vertical-injection structure with chip dimensions of 1.8 mm × 1.8 mm. InGaN/GaN short-period superlattice (SL) structures are employed below multiple-quantum-well active region as current spreading layers. It is found, by simulation, that SL layers are quite effective in improving current spreading and uniformity in carrier distribution. When the characteristics of the fabricated LED package are measured under pulsed operation conditions, efficiency droop is found to be greatly reduced in the LED structure with SL layers. A record high light output power of 4.18 W and external quantum efficiency of 51% are demonstrated at 3-A injection current.

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High resolution x-ray diffraction, electron beam induced current, capacitance-voltage profiling, admittance spectroscopy, deep level transient spectroscopy (DLTS), microcathodoluminescence (MCL) spectra and imaging were performed for multi-quantum-well (MQW) GaN/InGaN p-n junctions grown on epitaxial laterally overgrown (ELOG) n-GaN platform layers. These experiments show a very good crystalline quality of the MQW ELOG GaN/InGaN structures with a dislocation density of ∼106 cm−2 in the laterally overgrown ELOG wings regions. Admittance and DLTS spectra show the presence of a prominent electron-trap signal with activation energy ∼0.4 eV likely originating from electron activation from the lowest occupied state in the quantum wells. MCL spectra clearly show a redshift of luminescence in the laterally grown ELOG wings compared to the normally grown ELOG windows. Modeling based on solving Poisson–Schroedinger equations suggests that the main reason for the observed redshift is a higher indium content in the w...