Recently, achieving flexible and highly efficient light‐emitting elements is the most noticeable demand for lighting or displays. Here, fully flexible gallium nitride (GaN) light‐emitting diodes (LEDs) are demonstrated based on a unique transfer method. The LED structure consisting of GaN pyramid arrays are first fabricated on an amorphous glass‐based template with a low‐temperature gallium nitride/titanium (LT‐GaN/Ti) hetero‐interface, then released and embedded into a flexible or stretchable substrate using a specialized interface control. Nanovoids created during thermal annealing render the hetero‐interface weaker than the other interfaces. This interface is further weakened by a post‐mechanical treatment for gentle release of the GaN pyramid arrays from the interface during a transfer process. The LEDs typically have a total thickness of }70 lm and exhibit stable surface‐emitting electroluminescence even at a bending radius of }2 mm with exceptionally high luminance values of 595 and 175 cd/m2 at peak wavelengths of 514 and 483 nm, respectively. The results suggest a route to high brightness, large, flexible/stretchable blue or green lighting or displays.

We report color-selective photodetection from intermediate, monolayered, quantum dots buried in between amorphous-oxide semiconductors. The proposed active channel in phototransistors is a hybrid configuration of oxide-quantum dot-oxide layers, where the gate-tunable electrical property of silicon-doped, indium-zinc-oxide layers is incorporated with the color-selective properties of quantum dots. A remarkably high detectivity (8.1 × 1013 Jones) is obtained, along with three major findings: fast charge separation in monolayered quantum dots; efficient charge transport through high-mobility oxide layers (20 cm2 V−1 s−1); and gate-tunable drain-current modulation. Particularly, the fast charge separation rate of 3.3 ns−1 measured with time-resolved photoluminescence is attributed to the intermediate quantum dots buried in oxide layers. These results facilitate the realization of efficient color-selective detection exhibiting a photoconductive gain of 107, obtained using a room-temperature deposition of oxide layers and a solution process of quantum dots. This work offers promising opportunities in emerging applications for color detection with sensitivity, transparency, and flexibility.

No abstract

The photoresponse in graphene has drawn significant attention for potential applications owing to its gapless linear electronic band structure. To enhance both the spectral selectivity and responsivity in graphene, we demonstrate a novel but versatile and simple method of introducing surface plasmons. We utilize block copolymers to fabricate different nanostructured metal nanoparticle arrays on a single graphene surface. The plasmonic resonances could be tuned using Ag, Au, and Cu metal nanoparticles. By extending the synthetic route for the metallic particles, dual surface plasmonic bands from a single material were also successfully realized. Furthermore, enhanced photoresponsivity through the entire visible spectra could be achieved by mixing metallic nanoparticles and by controlling their shapes. Owing to its all-band transition characteristics, the ultrabroad band photocurrent generation in graphene can be tailored for an arbitrary photoresponse, which could be utilized in flexible CMOS image sensors (CIS) or other optoelectronic devices in the future. G raphene, a two-dimensional network of carbon atoms in a honeycomb lattice, has been intensively studied for the past decade owing to its unique optical and electronic properties in both fundamental science and applications. 1−6 Numerous studies have proven that the linear, gapless band structure of graphene surpasses the performance of currently available semiconductor-based electronic and optical devices on the market; in other words, unlike other superconductors, the ultrahigh mobility 1,7 and ultrabroad-band photoresponse originated by the all-band transition in graphene can be substantially modified through electrical gating. 8,9 Photocurrent generation in graphene has been observed at the graphene/metallic electrode junction, 10−12 at the p-/njunction formed on graphene by top gating, 12−14 and at the interface of graphene and various materials in the heterostructure. 15−24 Graphene-based interband photodetectors have been demonstrated from the ultraviolet, visible to mid-infrared (mid-IR) range, covering all optical communication bands. 16 Photocurrent at the metal−graphene junction and graphene p− n junctions has been described as either photovoltaic 10,12 or thermoelectric. 25 However, it is challenging to identify photovoltaic and thermoelectric currents in metal−graphene or graphene p−n junctions due to its identical polarity. Recently, in biased graphene, the thermoelectric effects are insignificant, but the photovoltaic and photoinduced bolometric effects dominate the photoresponse. 12 The property of the linearly dispersive and zero band gap, however, leads to a low density of states and no spectral selectivity. Therefore, there have been efforts to improve the low responsivity of graphene-based photodetectors by enhancing the light absorption with the aid of localized surface plasmon enhancement 26−28 or by near-field coupling with guided waveguides. 20−22 Recently, the responsivity was significantly increased by 3 orders of magnitude over that...

We examine exciton recombination, energy-, and charge transfer in multilayer CdS/ZnS quantum dots (QDs) on silver plasmonic resonators using photoluminescence (PL) and excitation spectroscopy along with kinetic modeling and simulations. The exciton dynamics including all the processes are strongly affected by the separation distance between QDs and silver resonators, excitation wavelength, and QD film thickness. For a direct contact or very small distance, interfacial charge transfer and tunneling dominate over intrinsic radiative recombination and exciton energy transfer to surface plasmons (SPs), resulting in PL suppression. With increasing distance, however, tunneling diminishes dramatically, while long-range exciton-SP coupling takes place much faster (>6.5 ns) than intrinsic recombination (~200 ns) causing considerable PL enhancement. The exciton-SP coupling strength shows a strong dependence on excitation wavelengths, suggesting the state-specific dynamics of excitons and the down-conversion of surface plasmons involved. The overlayers as well as the bottom monolayer of QD multilayers exhibit significant PL enhancement mainly through long-range exciton-SP coupling. The overall emission behaviors from single- and multilayer QD films on silver resonators are described quantitatively by a photophysical kinetic model and simulations. The present experimental and simulation results provide important and useful design rules for QD-based light harvesting applications using the exciton-surface plasmon coupling.