조용훈 교수

We report temperature-dependent time-integrated and time-resolved photoluminescence (PL) studies of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous emission behavior, specifically an S-shaped (decrease–increase–decrease) temperature dependence of the peak energy (Ep) for InGaN-related PL with increasing temperature: Ep redshifts in the temperature range of 10–70 K, blueshifts for 70–150 K, and redshifts again for 150–300 K with incre

Graphene quantum dot (GQD) light-emitting diodes (GQD-LEDs) are shown to have an electroluminescence exceeding 1000 cd m-2. These devices are possible due to a novel synthesis method to create GQDs with minimal oxidation, guaranteeing high quantum yields via the solvothermal formation of graphite intercalation compounds between graphite powder and sodium potassium tartrate. The GQDs are incorporated into polymeric host layers in a multilayer device and irradiate blue (~400 nm) emission. With str

High-performance, monolithic photoactivated gas sensors based on the integration of gas-sensitive semiconductor metal oxide nanowires on micro light-emitting diodes (μLEDs) are introduced. The μLEDs showed improved irradiance and energy conversion efficiency (i.e., external quantum efficiency, EQE), as the size of LEDs was reduced from 200 × 200 μm² (irradiance of 46.5 W/cm² and EQE of 4%) to 30 × 30 μm² (irradiance of 822.4 W/cm² and EQE of 9%). Gas-s

We present a comprehensive study of the optical characteristics of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}\mathrm{}$ epilayers $(0<~x<~0.6)$ by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. For ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}\mathrm{}$ with large Al content, we observed an anomalous PL temperature dependence: (i) an ``S-shaped'' PL peak energy shift (decrease-increase-decrease) and (ii) an ``inverted S-s

We have systematically studied the influence of Si doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. The twelve- period MQWs were grown by metalorganic chemical vapor deposition. Si doping in the GaN barriers was varied from 1×1017 to 3×1019 cm−3. Information on the structural quality of the MQWs as a function of Si doping was extracted fro

Electrically driven quantum dot, wire, and well hybrid light-emitting diodes are demonstrated by using nanometer-sized pyramid structures of GaN. InGaN quantum dots, wires, and wells are formed at the tops, edges, and sidewalls of pyramids, respectively. The hybrid light-emitting diodes containing low-dimensional quantum structures are good candidates for broad-band highly efficient visible lighting sources.

Influence of the size of indium clusters on optical properties of green-light-emitting InGaN quantum wells (QWs) was investigated by photoluminescence (PL), cathodoluminescence, PL excitation, and time-resolved PL techniques. Low luminescence efficiency was observed for green-light-emitting InGaN QWs with micron-sized indium clusters, in contrast to the case of InGaN QWs with submicron-sized small indium segregation. Both the thermal activation energy and the carrier lifetime dramatically decrea

Enhancing the fluorescence intensity of colloidal quantum dots (QDs) in case of color-conversion type QD light-emitting devices (LEDs) is very significant due to the large loss of QDs and their quantum yields during fabrication processes, such as patterning and spin-coating, and can therefore improve cost-effectiveness. Understanding the enhancement process is crucial for the design of metallic nanostructure substrates for enhancing the fluorescence of colloidal QDs. In this work, improved color

We have studied the anti-Stokes photoluminescence (ASPL) of a type-II ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{A}\mathrm{s}\ensuremath{-}\mathrm{G}\mathrm{a}\mathrm{I}\mathrm{n}\mathrm{P}}_{2}$ heterojunction. We have found that the ASPL can appear in both layers adjacent to the heterojunction when the excitation photon energy is higher than the energy of below-band-gap (BBG) luminescence. The intensity of ${\mathrm{GaInP}}_{2}$-related ASPL shows an almost linear dependence on

We report the structural properties of InGaN/GaN/AlGaN multiple quantum wells (MQWs) by means of two-dimensional reciprocal space mapping (RSM) of high resolution x-ray diffraction. The influence of Si doping in GaN barriers on the characteristics has been studied for 12-period MQWs grown by metalorganic chemical vapor deposition, which have different Si doping concentrations in the GaN barriers ranging from 1×1017 to 3×1019 cm−3. Information on the structural quality of these MQWs was extracted