A5102988647- GaN-based semiconductor devices and materials
- Ga2O3 and related materials
- Semiconductor materials and devices
- Metal and Thin Film Mechanics
- Primate Behavior and Ecology
- Neuroendocrine regulation and behavior
- ZnO doping and properties
- Semiconductor Quantum Structures and Devices
- Acoustic Wave Resonator Technologies
- Animal Behavior and Reproduction
- Photocathodes and Microchannel Plates
- Insect and Arachnid Ecology and Behavior
- Circadian rhythm and melatonin
- Nanoplatforms for cancer theranostics
- Organic Electronics and Photovoltaics
- Advanced Optical Imaging Technologies
- Advanced Fluorescence Microscopy Techniques
- Random lasers and scattering media
- Optical Coatings and Gratings
- Photoacoustic and Ultrasonic Imaging
- Orbital Angular Momentum in Optics
- Nonlinear Optical Materials Studies
- Cephalopods and Marine Biology
- Organic Light-Emitting Diodes Research
- Conducting polymers and applications
Ulsan National Institute of Science and Technology
2019-2025
University of Ulsan
2024
Sun Moon University
2013-2014
Kansas State University
2001-2006
With a recently developed unique deep ultraviolet picoseconds time-resolved photoluminescence (PL) spectroscopy system and improved growth technique, we are able to determine the detailed band structure near Γ point of wurtzite (WZ) AlN with direct gap 6.12 eV. Combined first-principles calculations show that fundamental optical properties differ drastically from GaN other WZ semiconductors. The discrepancy in energy values obtained previously by different methods is explained terms...
Deep UV photoluminescence spectroscopy has been employed to study the optical properties of AlxGa1−xN alloys (0⩽x⩽1). The emission intensity with polarization E⊥c and degree were found decrease increasing x. This is a consequence fact that dominant band edge in GaN (AlN) E⊥c(E∥c). Our experimental results suggest decreased efficiency related emitters could also be their unique property, i.e., light decreases It thus concluded AlGaN as active layers have very different from InGaN other...
Mg-doped AlN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in epilayers. From PL emission spectra and temperature dependence of intensity, a binding energy 0.51 eV for Mg acceptor was determined. Together with previous experimental results, activation AlxGa1−xN as function Al content (x) extrapolated entire composition range. The...
Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in AlxGa1−xN (0⩽x⩽1) epilayers. Two groups of were observed, which are assigned the recombination between shallow donors and two different level acceptors involving cation vacancies (Vcation) Vcation complexes alloys. These acceptor levels pinned energy common alloys (0⩽x⩽1). The related with observed x=0 1, while those only x=0.58 1. This points out fact that formation is more...
AlN epilayers with high optical qualities have been grown on sapphire substrates by metalorganic chemical vapor deposition. Deep ultraviolet photoluminescence (PL) spectroscopy has employed to probe the quality as well transitions in epilayers. Band-edge emission lines observed both at low and room temperatures are 6.017 6.033 eV 10 K. It was found that peak (integrated) intensity of deep impurity related transition is only about 1% (3%) band-edge temperature. The PL properties compared...
Al x Ga 1−x N alloys with up to 0.7 were grown by metalorganic chemical vapor deposition and their optical properties investigated deep UV time-resolved photoluminescence (PL) spectroscopy. Our results revealed that both the activation energy of PL emission intensity decay lifetime exhibit sharp increases at around 0.4. The can be understood in terms increase impurity binding or carrier/exciton localization x=0.4. A three orders magnitude resistivity undoped AlGaN 0.4 was also observed,...
AlN epilayers with high optical qualities have been obtained by metalorganic chemical vapor deposition on sapphire substrates. Deep UV picosecond time-resolved photoluminescence (PL) spectroscopy has employed to study the transitions in epilayers. Two PL emission lines associated donor bound exciton (D0X, or I2) and free (FX) observed, from which binding energy of excitons was determined be around 16 meV. Time-resolved measurements revealed that recombination lifetimes I2 were 80 50 ps,...
Si-doped n-type AlxGa1−xN alloys were grown by metalorganic chemical vapor deposition on sapphire substrates. We have achieved highly conductive for x up to 0.7. A conductivity (resistivity) value of 6.7 Ω−1 cm−1 (0.15 Ω cm) (with free electron concentration 2.1×1018 cm−3 and mobility 20 cm2/Vs at room temperature) has been Al0.65Ga0.35N, as confirmed Hall-effect measurements. Our experimental results also revealed that (i) the continuously increases with an increase Si doping level a fixed...
Nonlinear microscopy provides excellent depth penetration and axial sectioning for 3D imaging, yet widespread adoption is limited by reliance on expensive ultrafast pulsed lasers. This work circumvents such limitations employing rare-earth doped upconverting nanoparticles (UCNPs), specifically Yb3+/Tm3+ co-doped NaYF4 nanocrystals, which exhibit strong multimodal nonlinear optical responses under continuous-wave (CW) excitation. These UCNPs emit multiple wavelengths at UV (λ ≈ 450 nm), blue...
In x Al y Ga 1−x N quaternary alloys with different and compositions were grown by metalorganic chemical vapor deposition. Optical properties of these studied picosecond time-resolved photoluminescence. It was observed that the dominant optical transition at low temperatures in InxAlyGa1−xN due to localized exciton recombination, while localization effects combined from those InGaN AlGaN ternary comparable compositions. Our studies have revealed lattice matched GaN epilayers (y≈4.8x) highest...
Deep ultraviolet photoluminescence spectroscopy has been employed to study the optical transitions in AlN and GaN epilayers at temperatures from 10 800K, which parameters that describe temperature variation of energy band gap (α β or aB θ) linewidth broadening have obtained. These are compared with previously reported values obtained by different methods narrower ranges. Our experimental results demonstrate broader range measurements is necessary obtain accurate these parameters,...
AlN layers grown on Al2O3 substrates by metalorganic chemical vapor desposition were implanted with high doses (3×1016 cm−2, 250 keV) of Co+, Cr+, or Mn+. Band-edge photoluminescence intensity at ∼6 eV was significantly reduced the implant process and not restored 950 °C annealing. A peak observed 5.89 in all samples. Impurity transitions 3.0 4.3 both unimplanted AlN. X-ray diffraction showed good crystal quality for annealed samples, no ferromagnetic second phases detected. The Cr-...
The charge balance mechanism in green fluorescent organic light-emitting diodes is investigated for different electron transport layers (ETLs) and mobilities. Carrier accumulation an increase the exciton recombination probability are shown to be critical improving current power efficiencies by aligning bands at interface between emitting layer (EML) ETL. peak electroluminescence (EL) spectra was found shift slightly response changes width of emission zone reflected mobility Higher resulted a...
Despite the unique advantages of optical microscopy for molecular specific high resolution imaging living structure in both space and time, current applications are mostly limited to research settings. This is due aberrations multiple scattering that induced by inhomogeneous refractive boundaries inherent biological systems. However, recent developments adaptive optics wavefront shaping have shown not fundamentally only observation single cells, but can be significantly enhanced realize deep...
Si-doped AlN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates. Deep ultraviolet picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in epilayers. The donor bound exciton (or I2) transition was found be dominant recombination line at 10 K and its emission intensity decreases with increasing Si dopant concentration. Doping-induced PL linewidth broadening band-gap renormalization effects have also...
AlN epilayers grown by metalorganic chemical vapor deposition were implanted with cobalt ions and studied deep UV photoluminescence (PL). A PL emission peak at 5.87 eV (at 10 K) was observed for the Co-implanted epilayers, which absent in as-grown epilayers. Temperature dependence of intensity line revealed an ion-implantation induced defect energy level about 260 meV below conduction band. The is believed due to a band-to-impurity transition involving nitrogen vacancy (VN) ion-implanted...
Focusing through scattering media is a subject of great interest due to its direct impact in the field biomedical optics. However, greatest barrier currently limiting applications fact that most we wish deliver light are dynamic. To focus or dynamic media, using digital micromirror device (DMD) has been demonstrated be potential solution, as it enables fast modulation speeds. since DMD binary amplitude modulator, large number controlled modes needed acquire adequate enhancement limited...
AlN/GaN multiple quantum wells (MQWs) with a well thickness of 26 Å have been grown by metal–organic chemical-vapor deposition. A specially designed photoluminescence (PL) spectroscopy system, which is capable measuring picosecond time-resolved PL up to 6.2 eV, has employed probe the optical properties as carrier transfer and decay dynamics in these MQWs. Optical transitions at 4.039 5.371 eV T=10 K, resulting from interband recombination between electrons holes n=1 n=2 subbands wells,...
The recombination dynamics of optical transitions as well strain effects in AlInGaN/In0.08Ga0.92N quantum wells (QWs) were studied. QW emission energy, photoluminescence decay behavior, line shape, and nonradiative behavior found to be strong functions localization. degree carrier localization was inferred by modeling several aspects obtained from variable temperature time-resolved experiments. According the results, a minimum for unstrained QWs increased either tensile or compressive...
Mg -doped AlN epilayers grown by metalorganic chemical-vapor deposition have been studied deep ultraviolet time-resolved photoluminescence (PL) spectroscopy. A PL emission line at 6.02eV has observed 10K in Mg-doped AlN, which is about 40meV below the free-exciton transition undoped epilayer. Temperature dependence of intensity this also reveals a binding energy 40meV. This believed to be due recombination an exciton bound neutral acceptor (I1) with Ebx=40meV. value 10% level impurity...
Spatial light modulators (SLMs) have become an indispensable element in modern optics for their versatile performance many applications. Among various types of SLMs, such as digital micromirror devices (DMD), liquid crystal-based phase-only spatial (LC-SLMs), and deformable mirrors (DM), LC-SLMs are often the method choice due to high efficiency, precise phase modulation, abundant number effective pixels. In general, research grade applications, additional SLM calibration step is required...
Mouse sperm has a falciform apical hook at the head of sperm. In this study, we investigated function while migrating through female reproductive tract in Mus musculus (C57BL/6), using custom-built two-photon microscopy. Our observations indicate that plays probe-like role to facilitate interaction with epithelium during migration and an anchor-like secure onto epithelia uterine oviduct. We found no direct evidence trains being beneficial their migration. While may be key for cooperative...