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We investigated the optical and electrical properties of Ta2O5/Ag/Ta2O5 films as functions of the thicknesses of the Ta2O5 and Ag layers. It was found that with an increase in the thicknesses of the Ta2O5 and Ag layers from 10 to 40 nm and from 12 to 24 nm, respectively, the sheet resistance, carrier concentration, electron mobility, and resistivity of the Ta2O5/Ag/Ta2O5 film varied from 2.02 to 8.95 Ω/sq, 5.74 × 1021 to 2.92 × 1022 cm–3, from 13.21 to 24.07 cm2/V·s, and from 8.89 × 10-6 to 8.24 × 10-5 Ω cm, respectively. The average transmittance (Tav) of the multilayer samples ranged from 57.18% to 93.99%, and it depended on the Ta2O5 and Ag layer thicknesses. The highest Tav of 93.99% was observed for the film with 35 nm thick Ta2O5 and 18 nm thick Ag layers, and the peak Haacke's figure of merit (157.04 × 10–3 Ω–1) was obtained for 20 nm thick Ta2O5 and 21 nm thick Ag layers. Ta2O5 (100 nm) and Ta2O5/Ag/Ta2O5 (20 nm/21 nm/20 nm) samples had optical bandgaps of 4.70 and 4.45 eV, respectively. Film Wizard simulations were conducted to understand the dependence of the transmittance of the multilayer on the thicknesses of the Ta2O5 and Ag layers, and phasor analyses were performed to determine how the transmittance of the Ta2O5/Ag/Ta2O5 (20 nm/21 nm/20 nm) film depended on the Ta2O5 layer's thickness.

Dominant changes in structural, optical, and magnetic properties were observed at the highest dose of implanted ions with larger ionic radii which is due to the large number of produced defects in the host.

In this study, two-channel thin-film transistors (TC TFTs) using sputtered-deposited amorphous indium-gallium-zinc oxide (a-IGZO) as a channel layer and atomic-layer-deposition Al₂O₃ as gate insulator (GI) are proposed for wearable and portable device application. Symmetric-TC (S-TC) TFT structure consisted of conventional bottom gate (BG) TFT stacked on top of top gate (TG) TFT. Asymmetric-TC (A-TC) TFT contained BG TFT with tandem structure on the TG TFT. It was shown that the TC TFTs exhibited excellent performance such as high field-effect mobility ( $μ_{FE}$ ) and on/off current ratio ( $I_{t{on/off}}$ ) at low voltages (

We fabricated a 1 × 10 PbS QD photodiode array with multiple stacked QD layers with high-resolution patterning using a customized photolithographic process. The array showed the average responsivity of 5.54 × 10−3 A/W and 1.20 × 10−2 A/W at 0 V and -1 V under 1310- nm short-wavelength infrared (SWIR) illumination. The standard deviation of the pixel responsivity was under 10%, confirming the uniformity of the fabrication process. The response time was 2.2 ± 0.13 ms, and the bandwidth was 159.1 Hz. A prototype 1310-nm SWIR imager demonstrated that the QD photodiode-based SWIR image sensor is a cost-effective and practical alternative for III-V SWIR image sensors.

We report the effect of oxidation on PbS quantum dot (QD) photodetectors using rapid thermal annealing (RTA) and furnace annealing in air at different durations and temperatures. Air-annealed QD fi...

We investigated the thermal and optical characteristics of AgCu alloy disc (250 and 380 nm in diameter) arrays to produce an optical filter with low near infrared (NIR) transmittance, and compared their properties with those of Ag disc array. Unlike the Ag discs, the AgCu discs remained relatively stable with hillocks after annealing at 500 °C. The Ag and AgCu disc samples had similar transmittance characteristics, showing a global minimum at ~767 nm (for the 250 nm-disc samples) and at ~1081 nm (for the 380 nm-disc samples). Based on finite-difference time-domain (FDTD) simulations, the global minimum was related to localised surface plasmon resonance (LSPR). The Maxwell-Garnett model was employed to interpret the red-shift of the transmittance minima. The calculations showed that a mixture of agglomerated and stable Ag discs, resulting in different n and k values, would be responsible for the red-shift and an increase in the minimum transmittance.

We report on the development of high-performance transparent conducting GaSnO (GTO)/Ag/GTO multilayer electrodes for display applications. The optical and electrical characteristics of the GTO/Ag/GTO multilayers were investigated as functions of GTO layer (dGTO) and Ag layer (dAg) thicknesses. With increasing dGTO from 10 to 50 nm, the sheet resistance slightly increased from 3.83 to 4.81 Ω/sq, the carrier concentration decreased from 4.76 × 1022 to 1.12 × 1022 cm−3, and the mobility (μ) slightly changed from 10.7 to 10.3 cm2/V. The 40 nm-thick GTO-based multilayer exhibited the mean transmittance (Tav) of 91.6% and had the Haacke's figure of merit (FOM) of 87.84 × 10−3 Ω−1. The μ value increased from 7.97 to 11.67 cm2/V and sheet resistance varied from 7.81 to 3.47 Ω/sq as increasing dAg from 9 to 15 nm. The Tav of the GTO (40 nm)/Ag/GTO (40 nm) samples decreased from 94.5% to 84.9% with increasing dAg. The optical bandgaps of the GTO and GTO/Ag/GTO (40 nm/12 nm/40 nm) films were estimated to be 4.06 and 3.94 eV, respectively. Finite-difference time-domain calculations were conducted to explain the dAg and dGTO dependent transmittance of the GTO/Ag/GTO samples. With the phasor analyses, the dGTO dependence of the transmittance of GTO/Ag (12 nm)/GTO multilayers is described and discussed. Furthermore, the optical and electrical features of the optimal GTO/Ag/GTO (40 nm/12 nm/40 nm) electrode are compared with those of sputter-deposited 92 nm-thick indium tin oxide (ITO) films.

This Letter describes the impact of shape on micro light-emitting diodes (µLEDs), analyzing 400 µm2 area µLEDs with various mesa shapes (circular, square, and stripes). Appropriate external quantum efficiency (EQE) can yield internal quantum efficiency (IQE) which decreases with increasing peripheral length of the mesas. However, light extraction efficiency (ηe) increased with increasing mesa periphery. We introduce analysis of Jpeak (the current at peak EQE) since it is proportional to the non-radiative recombination. Etching the sidewalls using tetramethylammonium hydroxide (TMAH) increased the peak EQE and decreased the sidewall dependency of Jpeak. Quantitatively, the TMAH etching reduced non-radiative surface recombination by a factor of four. Hence, shrinking µLEDs needs an understanding of the relationship between non-radiative recombination and ηe, where analyzing Jpeak can offer new insights.

We investigated the effect of plasma-etching on the electrical and optical performance of lateral AlGaInP-based red micro-LEDs as a function of etching time, where plasma-etched Ag particles were used as masks. For the sample etched for 12 s, around 33% of the sample surface were randomly etched, whereas for the sample etched for 24 s, nearly 60% were randomly etched with additional nanoscale hillocks. Regardless of etching times, all samples exhibited similar forward voltages of 1.944–1.929 V at $20~\mu \text{A}$ and reverse leakage currents of $1\times 10^{-8}$ A at −10 V. The micro-LEDs fabricated with 12 s-etched and 24 s-etched $p$ -GaP gave 26.2% and 42.3% higher light output powers at $20~\mu \text{A}$ , respectively, than the one with unetched $p$ -GaP. The $S$ parameter decreased with increasing forward current and etching time. The electroluminescence (EL) peak intensities of the micro-LEDs were consistent with their light output performance and included shoulder peaks at 612 nm. Emission images showed that the micro-LEDs with the 24 s-etched $p$ -GaP revealed the most intense and uniform emission area among the three samples.

Sputter-deposited SrVOx was employed to create transparent conducting SrVOx/Ag/SrVOx films and their optical-electrical properties were examined as functions of SrVOx and Ag thicknesses. With the increase in the thickness of SrVOx films from 15 to 45 nm in the SrVOx/Ag/SrVOx films, the carrier concentration, sheet resistance, and electron mobility were in the range of 2.0 × 1022 − 1.03 × 1022 cm−3, 3.15−2.76 Ω/sq., and 21.99−19.76 cm2/Vs, respectively. The 25 nm-thick SrVOx-based multilayer gave the highest average transmittance (Tav) of 91.5%. The 25 nm-thick SrVOx-based multilayer gave the largest Haacke's figure of merit (FOM) of 144.5 × 10−3 Ω−1. With increasing Ag layer thickness from 9 to 21 nm, the carrier concentration, mobility and sheet resistance of the multilayers were in the range of 1.05 × 1022 − 1.99 × 1022 cm−3, 15.56−22.46 cm2/Vs, and 1.97−6.48 Ω/sq., respectively. The Tav of the SrVOx (25 nm)/Ag/SrVOx (25 nm) multilayer gradually decreased from 95.5 to 82.6% with the Ag layer thickness. The rigorous coupled-wave (RCW) simulations were performed to describe the wavelength-dependent transmittance characteristics of the SrVOx (25 nm)/Ag (15 nm)/SrVOx (25 nm) samples. Based on the phasor examination, the effect of the SrVOx film thickness on the transmittance characteristics of the multilayers is described and discussed.

We investigated how the performance and reliability of AlGaInP-based red (620 nm) micro-light-emitting diodes (micro-LEDs) ( $25\times 17\,\,\mu \text{m}^{2}$ ) were influenced by the use of $n$ -AlInP ohmic layer and distributed Bragg reflector (DBR). The AlGaAs-based DBR showed reflectivity of 94.9% at 622 nm with a 14 nm-stopband width. The micro-LEDs with $n$ -GaAs gave slightly lower forward voltages by 0.013 – 0.021 V than those with $n$ -Al0.5In0.5P/ $n$ -Al0.6Ga0.4As and $n$ -Al0.5In0.5P/DBR. However, the micro-LEDs with $n$ -Al0.5In0.5P/ $n$ -Al0.6Ga0.4As and $n$ -Al0.5In0.5P/DBR gave 61% and 125% higher light output power at $20~\mu \text{A}$ compared with that with $n$ -GaAs. It was shown that after annealing at 120 °C for 2,000 h, the forward voltage and the light output power at 4.7 A/cm2 of the micro-LEDs with $n$ -Al0.5In0.5P/DBR were degraded by 0.09% and 6.33%, respectively, with reference to those before annealing.

We report the fabrication of high-barrier-height and thermally reliable Schottky contacts to n-Al0.6Ga0.4N by using an Ag-Pd-Cu (APC) alloy. The Schottky barrier heights (SBHs) and ideality factors computed using the current-voltage (I–V) model ranged from 0.82 to 0.97 eV and from 3.15 to 3.44, respectively. The barrier inhomogeneity model and capacitance-voltage (C–V) method yielded higher SBHs (1.62–2.19 eV) than those obtained using the I–V model. The 300 °C-annealed APC sample exhibited more uniform electrical characteristics than the 500 °C-annealed Ni/Au Schottky samples (each with the best Schottky behavior). Furthermore, the scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) results indicated that the APC Schottky contacts were more thermally stable than the Ni/Au contacts. On the basis of the X-ray photoemission spectroscopy (XPS) results, the improved Schottky characteristics of the APC alloy contacts are described and discussed.

To fabricate a thermally stable optical filter in the mid-infrared (MIR) region, a plasmonic metal disk array (PMDA) using tantalum (Ta) was proposed, and the filter performance was compared with that of conventional silver (Ag)-based PMDAs. A finite-difference time-domain method was utilized to systematically analyze the effects of geometric configuration and constituent materials on the optical properties of PMDA filters with a periodic hexagonal lattice. Unlike the Ag PMDA filters, whose transmission dip at resonance wavelengths gradually decreased with increasing temperature, the Ta PMDA filters revealed almost the same transmission spectra even after annealing at 700 °C for 30 min. The Ta-based MIR PMDA filter exhibited similar optical properties to those of the Ag PMDA. The PMDAs with a duty cycle (d.c.) of 60% exhibited stop band spectra with sufficiently deep dip and wide linewidth. MIR filters fabricated with the Ta disks were demonstrated to quantify different types of alcohols through the monitoring of transmission spectra.

The electrosynthesis of formate from CO

We investigated the opto-electrical and electromigration properties of near ultraviolet light emitting diodes (UV-LEDs) fabricated with Ag–Pd–Cu (APC) and Ag only reflectors. It was shown that unlike Ag only sample, the APC sample revealed a smooth surface with hillocks when annealed at 600 °C. The 600 °C-annealed APC sample gave a reflectance of 84.2% at 400 nm, whereas the Ag sample had 69.0%. Both the samples exhibited ohmic behavior when annealed. The specific contact resistivity of the Ag and APC contacts annealed at 500 °C were estimated to be 2.59 × 10−4 and 1.85 × 10−4 Ωcm2, respectively. The X-ray photoemission spectroscopy Ga 2p core level results showed that for the annealed APC sample, the Ga 2p core level was shifted towards the lower binding-energies by 0.67 eV as compared to that of the as-deposited sample. Both UV-LEDs with the 500 °C-annealed Ag and APC reflectors gave the same forward voltage of 3.23 V at 20 mA. The UV-LED with the annealed APC reflector yielded 9.07% higher output at 100 mA than that with the annealed Ag reflector. The APC sample exhibited a longer median-time-to-failure (MTF) by a factor of 1.4 than the Ag sample. The activation energy for the electromigration of these samples was measured to be 0.58–0.7 eV. Electron back scatter diffraction (EBSD) and inverse pole figure (IPF) images revealed that the Ag sample was more -textured than the APC sample. Based on the scanning electron microscopy, EBSD and IPF results, the better thermal and electromigration properties of the APC sample are described and discussed.

The fabrication of ultra-high-resolution micro-displays with low power consumption is essential for applications in virtual reality and augmented reality systems. In this regard, GaN-based light-emitting diodes (LEDs) have been regarded as a promising candidate for self-emissive micro-displays. However, micro-LEDs suffer from sidewall defects and low quantum efficiency at a low current. Thus, we investigated the electrical and optical properties of InGaN-based green (520 nm) LEDs as functions of V pits and chip size. With decreasing chip size, the forward voltage of all samples increased at the same injection current. The samples with V pits exhibited markedly higher current density than those without V pits. With decreasing chip size, the current densities of all the samples increased, whereas the output power at the same current density decreased. As the chip size decreased, the peak external quantum efficiency of all the samples decreased, which was attained at high current densities. Furthermore, the samples with V pits displayed more efficient current spreading behavior, smaller ideality factors, and a smaller S parameter than the ones without V pits. The emission wavelength of the small samples (

Ag disc array (200 and 300 nm in diameter) was first adopted to realise the high-infrared-transmittance of ITO-based multilayers, whose array was defined by nanoimprint lithography. The electrical and optical properties of the ITO/Ag disc array/ITO samples were compared with ITO-only and ITO/Ag/ITO samples. Unlike the ITO/Ag/ITO sample, the transmittance of Ag disc array multilayer samples exhibited undulation in the visible region and large depression in the infrared spectral region. The 200-nm Ag disc, 300-nm Ag disc, ITO/Ag/ITO, and ITO-only samples had a transmittance of 20.8%, 95.1%, 32.5% and 86.8% at 982 nm, respectively. This implies that the transmittance in the IR region can be tuned by controlling size of the Ag discs. The sheet resistances of the Ag disc array, ITO/Ag/ITO, and ITO-only samples were 75.7–79.7, 4.77 and 147.96 Ω/sq., respectively. The Ag disc array samples showed mobilities of 32.11–33.91 cm2/V, while the ITO/Ag/ITO sample gave 17.45 cm2/V. The 200-nm Ag disc array sample exhibited higher Haacke's figure of merit (FOM) than the ITO/Ag/ITO sample. Finite-difference time-domain (FDTD) simulations were performed to understand the measured transmittance behaviour and the undulating transmittance of the Ag disc array samples was attributed to localised surface plasmon resonance (LSPR) effect.

We report on a simple and efficient process to enhance the performance of perovskite solar cells by using ITO electrodes with a nanoporous surface formed by wet-etching of self-agglomerated Ag nanoparticles. Effective removal of the Ag nanoparticles embedded in the surface of the ITO electrodes result in a nanoporous structure without changing the ITO's sheet resistance (10.17 Ω/square) and optical transmittance (89.08%) at a 550 nm wavelength. Examinations with a scanning electron microscope, a transmission electron microscope, and two-dimensional porous mapping show that the nanoporous ITO surface has an increased contact area with the electron transport layer, which enhanced the carrier extraction efficiency of the perovskite solar cells. Compare to perovskite solar cells fabricated on typical ITO with a flat surface morphology, the perovskite solar cells fabricated on the nanoporous-surface ITO show a higher fill factor of 81.1% and a power conversion efficiency of 20.1%. These results indicate that modified ITO surfaces with nano-scale porosity provide a simple and efficient method to improve the power conversion efficiency of perovskite solar cells without a complicated process.

By alloying GaN with AlN the emission of AlGaN light-emitting diodes can be tuned to cover almost the entire ultraviolet spectral range (210–400 nm), making ultraviolet light-emitting diodes perfectly suited to applications across a wide number of fields, whether biological, environmental, industrial or medical. However, technical developments notwithstanding, deep-ultraviolet light-emitting diodes still exhibit relatively low external quantum efficiencies because of properties intrinsic to aluminium-rich group III nitride materials. Here, we review recent progress in the development of AlGaN-based deep-ultraviolet light-emitting devices. We also describe the key obstacles to enhancing their efficiency and how to improve their performance in terms of defect density, carrier-injection efficiency, light extraction efficiency and heat dissipation. This Review covers recent progress in AlGaN-based deep-ultraviolet light-emitting devices. The key technologies of how to improve their performance, carrier-injection efficiency, light extraction efficiency and heat dissipation are discussed.

ITO/Ag/ITO multilayers were optimized at different annealing conditions and were employed as a current spreading layer (CSL) for 365 nm UVLEDs. The ITO (40 nm) layer gave a transmittance of 83.9% at 365 nm, while the ITO/Ag/ITO (13 nm/14 nm/23 nm) multilayers annealed at 600 °C in N2 ambient had 92.3%. The ITO/Ag/ITO multilayer annealed at 600 °C in N2 ambient yielded a sheet resistance of 3.8 Ω/sq., while the ITO layer had 186.8 Ω/sq. The ITO/Ag/ITO multilayers annealed at 600 °C had a Haacke's figure of merit (FOM) of 106.1 × 10−3 Ω−1, which was far larger than that of the ITO layer (1.5 × 10−3 Ω−1). The annealed multilayers revealed optical bandgaps of 3.74–3.94 eV. The high-angle annular dark-field images showed that unlike the N2-annealed samples, the Ag layer of the air-annealed sample experienced agglomeration. Ultraviolet light-emitting diodes (UVLEDs) fabricated with the 600 °C-annealed ITO/Ag/ITO CSL displayed 68.5% higher light output at 100 mA than the reference ITO UVLED. Unlike the UVLED with reference ITO, the UVLEDs with the annealed multilayers exhibited uniform light emission across the chip area. The higher light output was attributed to the combined effects of the high transmittance, and better current injection and current spreading of the annealed multilayers.

We investigated the effect of via-holes in the lead-frame on the reliability of blue flip-chip light-emitting diodes (FCLEDs). For bonding, conventional Sn-Ag(3.0%)-Cu(0.5%) solder (SAC) and Ag sintered paste were adopted. Lateral LED, conventional FCLED (c-FCLED), and via-hole FCLED gave efficacies of 218.5, 221.6 and 225 lm/W at 30 mA. The lateral LED sample (bonding material: silicone), c-FCLED sample (SAC), via-hole-type sample (Ag sinter), and via-hole-type sample (SAC) exhibited total thermal resistance of 15.24, 10.19, 8.95, and 11.79 K/W, respectively. The humidity/temperature/H2S gas reliability examinations showed that unlike the via-hole-type samples, the lumen of the c-FCLED was fallen by 15.0% after exposure for 500 h. Furthermore, the c-FCLED exhibited a 19.6% higher forward voltage than the via-hole FCLED after 1,000 thermal-cycles. SEM results showed that unlike the via-hole type FCLED, the c-FCLED underwent cracking after thermal cycle of 1000 times.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) formed layered van der Waals (vdW) crystals have emerged as promising candidates for varieties of potential applications, such as gas sensors, photodetectors, light-emitting diodes, Schottky diodes and memories, due to their unique physical features. However, since the existence of the metal-induced gap states (MIGS) at metal-semiconductor interfaces, it is severely difficult to adjust their electrical properties. It was demonstrated in previous researches that various metal contacts on TMDs semiconductor exhibit regular Schottky barrier height by Fermi-level pinning effect. In this study, we suggest the van der Waals material contact between TiS2 semimetal and WSe2 semiconductor for leading van der Waals gap at their interface. Through this approach, the TiS2/WSe2 2D heterojunction can efficiently address the MIGS. Interestingly, the TiS2/WSe2 heterojunction exhibits a novel electrical transport characteristics such as distinct ambipolar and rectifying behaviors by tuning drain voltage polarity. Firstly, under reverse bias (V ds < 0), TiS2/WSe2 heterojunction operates efficiently and allows transport of the carriers at both polarities of the gate voltage (V bg < 0 and V bg > 0), namely ambipolar behavior. Secondly, under the forward bias (V ds > 0), TiS2/WSe2 heterojunction does not allow transport of the electrons at positive gate voltage (V bg > 0), but allow transport of the holes at negative gate voltage (V bg < 0), namely p-type behavior. To understand the carrier transport mechanism of these results, ultra-violet photoelectron spectroscopy (UPS) measurements were also carried out on the WSe2 and TiS2 flakes. It is noted that the TiS2/WSe2 junction plays a crucial role in determining a novel electronic property of this device. Figure 1

We investigated the effect of Ti/Al and ITO/Ag n-type contacts on the emission uniformity and light output of different chip-size vertical-geometry light-emitting diodes (VLEDs) for vehicle headlamp application. The forward voltage of the Ti/Al-based reference VLEDs decreased from 3.38 to 3.20 V at 1500 mA with increasing chip size from (1280 × 1000 µm2) to (1700 × 1700 µm2), whereas that of the ITO/Ag-based samples changed from 3.37 to 3.15 V. Regardless of chip size, the ITO/Ag-based samples revealed higher light output power than the reference samples. For example, the ITO/Ag-based samples (chip size of 1700 × 1700 µm2) exhibited 3.4% higher light output power at 1500 mA than the reference samples. The ITO/Ag samples underwent less degradation in the Wall-plug efficiency (WPE) than the reference sample. For instance, the ITO/Ag-based samples (1700 × 1700 µm2) gave 4.8% higher WPE at 1500 mA than the reference samples. The ITO/Ag-based samples illustrated more uniform emission than the Ti/Al-based sample. Both the reference and ITO/Ag-based samples underwent no degradation when operated at 1500 mA for 1000 h.

Mid-infrared wavelengths are called the molecular fingerprint region because it contains the fundamental vibrational modes inherent to the substances of interest. Since the mid-infrared spectrum can provide non-destructive identification and quantitative analysis of unknown substances, miniaturized mid-infrared spectrometers for on-site diagnosis have attained great concern. Filter-array based on-chip spectrometer has been regarded as a promising alternative. In this study, we explore a way of applying a pillar-type plasmonic nanodiscs array, which is advantageous not only for excellent tunability of resonance wavelength but also for 2-dimensional integration through a single layer process, to the multispectral filter array for the on-chip spectrometer. We theoretically and experimentally investigated the optical properties of multi-periodic triangular lattices of metal nanodiscs array that act as stopband filters in the mid-infrared region. Soft-mold reverse nanoimprint lithography with a subsequent lift-off process was employed to fabricate the multispectral filter array and its filter function was successfully extracted using a Fourier transform infrared microscope. With the measured filter function, we tested the feasibility of target spectrum reconstruction using a Tikhonov regularization method for an ill-posed linear problem and evaluated its applicability to the infrared spectroscopic sensor that monitors an oil condition. These results not only verify that the multispectral filter array composed of stopband filters based on the metal nanodiscs array when combined with the spectrum reconstruction technique, has great potential for use to a miniaturized mid-infrared on-chip spectrometer, but also provide effective guidance for the filter design.

A synaptic device that contains weight information between two neurons is one of the essential components in a neuromorphic system, which needs highly linear and symmetric characteristics of weight update. In this study, a charge trap flash (CTF) memory device with a multilayered high-&kappa, barrier oxide structure on the MoS2 channel is proposed. The fabricated device was oxide-engineered on the barrier oxide layers to achieve improved synaptic functions. A comparison study between two fabricated devices with different barrier oxide materials (Al2O3 and SiO2) suggests that a high-&kappa, barrier oxide structure improves the synaptic operations by demonstrating the increased on/off ratio and symmetry of synaptic weight updates due to a better coupling ratio. Lastly, the fabricated device has demonstrated reliable potentiation and depression behaviors and spike-timing-dependent plasticity (STDP) for use in a spiking neural network (SNN) neuromorphic system.

As the size of micro light-emitting diodes ( μLEDs) decreases, μLEDs encounter etching damage especially at the sidewalls that critically affects their properties. In this study, we investigated the influence of etching bias power ( Pbias) on the performance of μLEDs and found that the current–voltage and light output–current characteristics of μLEDs were enhanced when Pbias was reduced. It was shown that at low Pbias, the chemical reaction between etching gas and gallium nitride, rather than ion sputtering, dominated the etching process, leading to low plasma damage and rough surface morphology. Additionally, to understand the etching-induced surface roughening behaviors, various substrates with different threading dislocation densities were treated at low Pbias. It was found that for the sample (with p-contact size of 10 × 10 μm2), the efficiency droop was approximately 20%, although the current reached 10 mA due most probably to the suppressed polarization effect in the quantum well. It was further observed that the external quantum efficiency (EQE) was dependent on Pbias, where the lowest Pbias yielded the highest maximum EQE, indicating that the plasma damage was mitigated by reducing Pbias. Optimization of dry etching and polarization-suppression conditions could pave the way for realizing high-performance and brightness μLEDs for next-generation displays.

For micro-light-emitting diode (LED)-based display applications, such as virtual reality and augmented reality, high-performance Ohmic contacts (namely, the improvement of current injection efficiency) is vital to the realization of high-efficiency micro-LEDs. The surface Fermi level pinning characteristics could be comprehended in terms of the relation between work function of metals (ΦM) and Schottky barrier height (SBH, ΦB). In this study, we have investigated the surface Fermi level pinning characteristics of (001) n-AlInP surfaces by employing Schottky diodes with different metals. With an increase in the temperature, ΦB increases linearly and ideality factors (n) decreases. This behavior is related to the barrier height inhomogeneity. Inhomogeneity-model-based ΦB is evaluated to be in the range of 0.86–1.30 eV, which is dependent on the metal work functions and are similar to those measured from capacitance-voltage relation. Further, The S-parameter, the relation between ΦB and ΦM (dΦB/dΦM), is 0.36. This is indicative of the partial pinning of the surface Fermi level at the surface states placed at 0.95 eV below the conduction band. Furthermore, it is also shown that (NH4)2S-passivation results in an increases the mean SBH and the S-parameter (e.g., 0.52).

Light extraction in organic light-emitting diodes (OLEDs) was improved by applying SnO

Extensive efforts have been devoted to improving the resolution of surface plasmon resonance (SPR) sensors in the detection of trace levels of biomolecules considered essential for the early diagnosis of disease. As part of these efforts, we previously developed a bimetallic waveguide-coupled surface plasmon resonance (Bi-WCSPR) sensor configuration designed to dramatically reduce the linewidth of the SPR curve while preserving a moderate local field decay length, thereby addressing the resolution issue. In this study, we systematically quantified the enhanced resolution in Bi-WCSPR sensors used to detect C-reactive protein (CRP), a widely accepted biomarker of inflammation in cardiovascular disease. Individual SPR sensorgrams were measured at several CRP concentrations in both the intensity and angular interrogation modes, confirming that the Bi-WCSPR configuration with a high Ag-to-Au ratio provided a figure-of-merit (FOM) that was 2.53 times higher than that of conventional Au sensors and a limit-of-detection (LOD) that was an order of magnitude lower than the cut-off level for CRP. It was found that when using the Bi-WCSPR configurations, the resolution enhancement in the intensity interrogation mode becomes more evident as the CRP concentrations is lowered to the cut-off level.

We report the characteristics of Sn-doped In2O3 (ITO) films intended for use as transparent conducting electrodes; the films were prepared via a five-generation, in-line type, cylindrical, rotating magnetron sputtering (CRMS) system as a function of film thickness. By using a rotating cylindrical ITO target with high usage (∼80%), we prepared high conductivity, transparent ITO films on five-generation size glass. The effects of film thickness on the electrical, optical, morphological, and structural properties of CRMS-grown ITO films are investigated in detail to correlate the thickness and performance of ITO films. The preferred orientation changed from the (2 2 2) to the (4 0 0) plane with increasing thickness of ITO is attributed to the stability of the (4 0 0) plane against resputtering during the CRMS process. Based on X-ray diffraction, surface field emission scanning electron microscopy, and cross-sectional transmission electron microscopy, we suggest a possible mechanism to explain the preferred orientation and effects of film thickness on the performance of CRMS-grown ITO films.

Light-emitting diodes (LEDs) have been widely applied for backlight unit for displays, general lighting, and automotive illumination because they have a high light efficiency and long life time, and are environmentally friendly. These diverse applications require smaller and slim LED chip scale packages (CSPs). CSP LEDs have been developed to produce white LED chips by forming a thin phosphor film on blue LED chips. In this study, we investigated the effect of phosphor layer thickness and area on the optical and thermal properties of the CSP LEDs. The phosphor-conversion of chips is maximized by varying the thickness and area of the phosphor layer. Eight different types of phosphor-converted white CSPs with normal performance (CRI > 70, CCT ~ 5700 K) were prepared by using mixed multicolor phosphor materials. In other words, for five samples whose CSP area was fixed at 1.8 x 1.8 mm2, flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the thickness of the phosphor layers was varied from 100 to 500 μm at intervals of 100 μm. For other three samples where the phosphor layer thickness was fixed at 300 μm, the flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the CSPs had three different areas of 1.6 x 1.6, 1.8 x 1.8, and 2.0 x 2.0 mm2. First, the relative luminous flux and LED beam distribution were characterized using integrating sphere and a goniometer. It was shown that as the thickness of the phosphor layer increased, the luminous flux and the directivity angle increased. On the other hand, as the CSP area increased, the luminous flux and the directivity angle decreased. This could be attributed to the fact that CSP does not have a reflector (namely, a housing material) and so the blue light of the chip does not excite the whole area of the phosphor. This may be confirmed by the images showing light distribution and luminescence characteristics, which is currently under investigation. Furthermore, a junction temperature measurement system was used to characterize the junction temperatures of the five different samples whose phosphor layer thicknesses were varied from 100 to 500 μm. It was found that when the thickness of the phosphor layer exceeded the thickness of the chips (250 μm), the junction temperature of the samples dramatically increased. Further details regarding the phosphor layer thickness of the junction temperature characteristics will be investigated and described.