Blueshift Of Peak Wavelength Research Articles

Size-dependent optoelectronic characteristics of InGaN/GaN red micro-LEDs on 4-inch Si substrates: high pixel density arrays demonstration

In this study, we explored the size-dependent optoelectronic characteristics of InGaN/GaN red micro-LEDs grown on Si substrates. We successfully demonstrated the fabrication of 4-inch wafer-scale InGaN/GaN micro-LEDs, showcasing the feasibility of large-scale production. Additionally, we presented the binary pixel display with 6 µm pitch, achieving a resolution of 4232 PPI. We also introduced a method of driving the display using PWM to linearly control and counteract the blue shift in peak wavelength caused by the QCSE and band-filling effect. Our research represents a significant milestone in the development of InGaN/GaN red micro-LEDs on Si substrates, establishing them as a key component for full-color micro-LED displays.

Improvement in quantum efficiency of green GaN-based micro-LED by trapezoidal quantum well

The main challenges in the application of GaN-based full-color micro-light-emitting diodes (micro-LEDs) are size-dependent effects and low quantum efficiency, especially for green micro-LEDs. In this study, we propose to use a trapezoidal quantum well (QW) structure in GaN-based green micro-LEDs. The trapezoidal QW structure is able to improve the electron hole wave function overlap, thus increasing the external quantum efficiency (EQE). Green micro-LEDs with active region size of 75 × 64 μm2 are fabricated by metal organic chemical vapor deposition. The peak EQE of the green trapezoidal QW micro-LED reaches 15.8% at a low injection current density of 0.6A/cm2, which is 1.96 times higher than that of conventional rectangular QW. The test results indicate that the trapezoidal QW structure greatly improves the quantum efficiency of green micro-LED, inhibits the blue shift of peak wavelength and improves color purity, which paves the way to single substrate full-color micro-LED display with high-performance. The technology proposed in this paper does not change the production line equipment, but improves the traditional process, so it is expected to significantly improve the external quantum efficiency of the existing green micro-LED under the existing equipment. The production technology of existing InGaN QW micro-LED is directly adopted, and the EQE can be further improved if some new dry etching and passivation methods are applied.

High selectivity and fluorescence reversible Eu3+ sensor based on GSH-capped AgZnInS QDs.

Fluorescence sensors for trivalent europium ions (Eu3+) are seldom reported. We study the synthesis of water-soluble quaternary quantum dots (QDs) and investigate their fluorescence sensor application for detecting Eu3+ The as-synthesized glutathione (GSH)-capped AgZnInS (AZIS) QDs show great sensitivity and selectivity to Eu3+among 12 different metal cations. Detailed experimental results indicate that the fluorescence response of the AZIS QDs to increasing concentration of Eu3+ ([Eu3+]) include intensity quenching and peak wavelength blueshift. With the addition of OH-, the fluorescence response reverses. Electron transfer is considered to be the mechanism for the fluorescence quenching and peak wavelength blueshift of the GSH-capped AZIS QDs. Our work provides a new, to the best of our knowledge, method for the detection of Eu3+.

Ultrasmall and ultradense InGaN-based RGB monochromatic micro-light-emitting diode arrays by pixilation of conductive p-GaN

We describe 5 μm squircle InGaN-based red, green, and blue (RGB) monochromatic micro-light-emitting diodes (μLEDs) with an interpitch of 4 μm by pixilation of conductive p-GaN using a H 2 -plasma treatment. The p-GaN was passivated by H 2 plasma and prevented the current’s injection into the InGaN quantum wells below. We observed that InGaN-based red μLEDs exhibited a broader full width at half-maximum and larger peak wavelength blueshift at 11.5 – 115 A / cm 2 than the green/blue μLEDs. The on-wafer light output power density of the red μLEDs at a wavelength of 632 nm at 115 A / cm 2 was approximately 936 mW/ cm 2 , the highest value reported thus far for InGaN-based red μLEDs. This value was comparable with that of the green/blue μLEDs at 11.5 A / cm 2 , indicating that the red μLEDs can satisfy the requirement of high brightness levels for specific displays. The color gamut based on InGaN RGB μLEDs covered 83.7% to 75.9% of the Rec. 2020 color space in the CIE 1931 diagram at 11.5 to 115 A / cm 2 .

Enhanced external quantum efficiency of III-nitride micro-light-emitting diodes using vertical and transparent package

In this work, 40 × 40 μm2 blue InGaN micro-light-emitting diodes (μLEDs) with transparent and vertical package was first demonstrated by using either double-side polished zinc oxide (ZnO) or sapphire substrate as a transparent submount. The performance of the vertical and conventional packages was compared, where the devices packaged vertically resulted in smaller blueshift in peak wavelength with increasing drive current due to the higher junction temperature. Moreover, devices packaged vertically with the sapphire submount offered 19% and 32% greater light output power at 20 and 100 A cm−2, respectively, and 18% improvement in maximum external quantum efficiency (EQE) than devices with conventional package. Finally, the peak EQE of 58% was achieved from the μLED packaged vertically using a sapphire submount.

Toward heteroepitaxially grown semipolar GaN laser diodes under electrically injected continuous-wave mode: From materials to lasers

III-nitrides based light-emitting diodes and laser diodes (LDs) have shown great success as solid-state lighting sources, but the development of common c-plane (0001) polar GaN emitters is facing limitations due to quantum-confinement Stark effect, efficiency drop, low efficiency at green range, and peak wavelength blue-shift. Efficient semipolar or nonpolar GaN light emitting diodes and LDs have been successfully demonstrated by growing on semipolar or nonpolar free-standing GaN substrates. The small size and high cost of high crystal quality semipolar or nonpolar free-standing GaN substrates, which are sliced from hydride vapor phase epitaxy grown c-plane bulk GaN substrate, have severely limited their commercial development and application. Achieving scalable heteroepitaxial semipolar GaN materials with a very low density of basal-stacking faults (BSFs) on a foreign substrate remains very challenging. The recent breakthrough in the demonstration of continuous-wave (CW) semipolar (202¯1) LDs at room-temperature on semipolar GaN/sapphire template marks a milestone in exploring high crystal quality heteroepitaxial semipolar GaN materials and low-cost semipolar emitters. Here, we review the key progress through the past years about the development of heteroepitaxial semipolar GaN materials including epitaxial lateral overgrowth, orientation controlling epitaxy, BSFs burying by neighboring Ga-polar (0001) GaN with air voids, facet-engineering orientation control epitaxy, resulting in a low density or free of basal stacking faults. Furthermore, we discuss the heteroepitaxially grown pulsed semipolar (112¯2) blue LDs and CW semipolar (202¯1) LDs.

Photoluminescence and Raman Scattering of GaAs1-xBix Alloy

Photoluminescence (PL) and Raman spectra of GaAs1-xBix samples grown at different rates (0.09 to 0.5 µm/h) were investigated. The PL peak wavelength initially redshifted with the increase of growth rate and reached the longest wavelength (1158 nm) for sample grown at 0.23 µm/h. This is followed by PL peak wavelength blueshift for higher growth rates. The Raman data show peaks at 162, 228, 270, and 295 cm-1 which can be attributed to GaAs like phonons. GaBi like vibrational modes were also observed at 183 and 213 cm-1. However, the intensity of Bi induced phonons is significantly weaker compared to GaAs due to low concentration of Bi compared to As and thin GaAs1-xBix epilayer. The PL data and GaAs transverse optical (TO) to longitudinal optical (LO) phonons intensity ratio indicate that Bi concentration is highly dependent on the growth rate and the highest Bi concentration was obtained by sample grown at 0.23 µm/h. It is found that the full-width-at-half-maximum (FWHM) of GaAs LO mode increases significantly for samples grown at high growth rates suggesting crystal quality degradation due to lack of surfactant effects.

Spectroscopic properties of various blood antigens/antibodies.

Since the traditional method generates biological waste, there is a significant demand for an easy, quick technique of blood type identification without contamination. In fact, individuals can be divided into four main blood groups whose antigens are available in red blood cell (RBC) membranes and the antibodies in the plasma. Here, UV-vis and photoluminescence (PL) spectroscopic methods are systematically used to find the spectra of blood typing antigens (A, B and AB) and antibodies i.e. A-Anti, B-Anti, AB-Anti and D reagent. The PL spectra of RBCs in different blood groups as well as the corresponding antibodies are successfully resolved for the purpose of blood typing. The unique photophysical characteristics of these biomolecules including signal intensity and peak emission wavelength in PL spectra are lucidly anticipated to accurately discriminate ABO groups. PL spectra of RBC in positive blood typing indicate larger signal and shorter emission peak wavelength corresponding to negative ones. Furthermore, the monoclonal antibody PL emissions emphasize that Anti-A benefits higher intensity and shorter peak wavelength (blue shift) than B-Anti. In the following, lucid blue shifts are obtained in terms of antibody concentrations accompanying the elevation of fluorescence signal, most likely due to the aggregation induced emission (AIE) phenomenon, quite the opposite of the aggregation-caused quenching (ACQ) that is widely observed from conventional chromophore. Those are envisaged as unique properties of each antibody to utilize in the spectral blood typing.

TiO2 DOPED PDPP3T NANOCOMPOSITE THIN FILM FOR PHOTOVOLTAIC APPLICATION

In present work, an inorganic dopant TiO2 nanoparticles are introduced into the PDPP3T polymer host material and deposited as thin films via spin coating. Different solvent are investigated to get efficient dispersion of TiO2 nanoparticles as well as effective dissolution of PDPP3T material. The role of TiO2 particles towards optical absorption of PDPP3T material is studied by preparing different PDPP3T/TiO2 blend ratios and annealed at different temperatures. Toluene is found an efficient solvent for the dispersion of TiO2 nanoparticles as well as dissolution of PDPP3T material. Significant increase in optical absorption in UV region 300-400nm is observed for the PDPP3T/TiO2 blend ratio 1:0.2 and the annealing temperature 310oC. The deposited thin film with four layers have demonstrated significant blue shift in peak wavelength and increase in the absorption in UV region (300-400nm). XRD analysis reveals amorphous nature of all deposited thin film. No significant variations in chemical structure are observed with increase in thickness of deposited layer. The addition of TiO2 particle in PDPP3T material significantly enhanced the optical absorption in UV region.

Characteristics of GaN-based 500 nm light-emitting diodes with embedded hemispherical air-cavity structure

GaN-based 500 nm light-emitting diodes (LEDs) with an air-cavity formed on a laser-drilled hemispherical patterned sapphire substrate (HPSS) were investigated. The cross-section transmission electron microscopy image of the HPSS-LED epilayer indicated that most of the threading dislocations were bent towards the lateral directions. It was found that in InGaN/GaN multiple quantum wells (MQWs) of HPSS-LEDs, there were fewer V-pits and lower surface roughness than those of conventional LEDs which were grown on flat sapphire substrates (FSSs). The high-resolution x-ray diffraction showed that the LED grown on a HPSS has better crystal quality than that grown on a FSS. Compared to FSS-LEDs, the photoluminescence (PL) intensity, the light output power, and the external quantum efficiency at an injected current of 20 mA for the HPSS-LED were enhanced by 81%, 65%, and 62%, respectively, such enhancements can be attributed to better GaN epitaxial quality and higher light extraction. The slightly peak wavelength blueshift of electroluminescence for the HPSS-LED indicated that the quantum confined Stark effect in the InGaN/GaN MQWs has been reduced. Furthermore, it was found that the far-field radiation patterns of the HPSS-LED have smaller view angles than that of the FSS-LED. In addition, the scanning near field optical microscope results revealed that the area above the air-cavity has a larger PL intensity than that without an air-cavity, and the closer to the middle of the air-cavity the stronger the PL intensity. These nano-light distribution findings were in good agreement with the simulation results obtained by the finite difference time domain method.

Temperature-induced spectrum response of volume grating as an effective strategy for holographic sensing in acrylamide polymer part I: sensing.

Temperature-induced diffraction spectrum responses of holographic gratings are characterized for exploring the temperature-sensing capability of a holographic sensor. Linear blue shift of peak wavelength and linear diffraction reduction are observed. It provides quantitative expressions for sensing applications. Inorganic nanoparticles are dispersed into the binder to improve sensing properties. Obvious improvement of sensing parameters, including wavelength shift and diffraction change, is confirmed. The sensitivity, response rate, and linear response region of holographic sensors are determined to evaluate sensing capacity. Influence of relative humidity on holographic sensing response is discussed. Expansion of humidity range provides a probability for extending the range of wavelength shift. Finally, the temperature response reversibility of a holographic sensor is evaluated. These experimental results can expand the practical application field of holographic sensing strategy and accelerate the development of holographic sensors.

Structure, luminescence and thermal quenching properties of Eu doped Sr2−xBaxSi5N8 red phosphors

Eu2+ doped Sr2-xBaxSi5N8 phosphors were synthesized at 1610℃ for 4h via the solid-state reaction method. The XRD results confirm that the complete solid solutions are formed. With the increase of x, the emission spectra show an obvious blue-shift from 610nm to 585nm under the excitation of 460nm. The color tone can be tuned from yellow to red. The corresponding mechanism for the blue-shift of peak-wavelength is studied in detail. The results of decomposed Gaussian spectra and fluorescence lifetime show that the local coordination structure surrounding activator ions changes with increasing x value. It is found that the probability of Eu occupying Sr1 and Sr2 site is dependent on Ba/Sr ratio. The variation of thermal quenching properties and the corresponding mechanism is discussed in detail. The results indicate that Eu2+ doped Sr2-xBaxSi5N8 is a promising orange red-emitting phosphor for near UV or blue light-pumped white light-emitting-diodes (wLEDs).

Green light emitting diode grown on thick strain-reduced GaN template

We report a green light-emitting diode (LED) grown on thick strain-reduced GaN template. As the injection current changes from 20mA to 120mA, blue-shift of EL peak wavelength reduces from 9.3nm for the LED on sapphire substrate to 6.8nm for the LED grown on thick strain-reduced GaN template. Furthermore, the light output power and external quantum efficiency of the LED on thick strain-reduced GaN template are respectively 1.48mW and 2.5% at the forward current of 20mA, which is twice as much as the LED on sapphire substrate. In contrast, the reverse current is 2μA lower than that of the LED on the sapphire at −8V.

Improvement on InGaN‐based light emitting diodes using p‐GaN layer grown at low temperature in full N2 environment

A method is suggested to improve the characteristics of light emitting diodes (LEDs) by using p‐GaN structure with heavily Mg‐doping grown at low temperature in full N2 environment. The LED exhibits a 36.4% enhancement in light output power (LOP) at 222 A cm−2 due to the higher hole concentration as compared to the normal p‐GaN layer. Meanwhile, the experimental results prove that the optimized LED structure shows reduced efficiency droop behavior, smaller peak wavelength blueshift and narrower electroluminescence (EL) spectrum broadening.

Current steering effect of GaN nanoporous structure

Current steering effect of InGaN light emitting diode (LED) structure was demonstrated by forming a high resistivity GaN nanoporous structure. Disk-array patterns with current-injection bridge structures were fabricated on InGaN LED devices through a focused ion beam (FIB) system. GaN nanoporous structure was formed around the FIB-drilled holes through a electrochemical (EC) wet-etching process on a n-type GaN:Si layer under the InGaN active layer. High emission intensity and small peak wavelength blueshift phenomenon of the electroluminescence spectra were observed in the EC-treated region compared with the non-treated region. The branch-like nanoporous structure was formed along the lateral etched direction to steer the injection current in 5μm-width bridge structures. In the FIB-drilled hole structure, high light emission intensity of the central-disk region was observed by enlarging the bridge width to 10μm, with a 5μm EC-treated width, that reduced the current steering effect and increased the light scattering effect on the nanoporous structure. The EC-treated GaN:Si nanoporous structure acted as a high light scattering structure and a current steering structure that has potential on the current confinement for vertical cavity surface emitting laser applications.

注入电流对绿光高压LED光电特性的影响

GaN-based green high-voltage(HV) light emitting diodes(LEDs) of 12 V were designed and fabricated.The optical and electrical parameters such as forward voltage,peak of wavelength,optical power,and luminous efficiency were investigated when the injection current varied from 3 mA to 50 mA at 25 ℃.The results show that the injection current has a great effect on the optical and electrical properties of the GaN-based high-voltage LED.When the current is 20 mA,the corresponding voltage is 14 V.With the increasing of the injection current,the blue-shift of LED peak wavelength reaches 2 nm.In addition,the optical power increases approximately linearly with the current increasing.The luminous efficiency decreases 61% when the injection current increases from 3 mA to 20 mA,and decreases 39% when the injection current increases from 20 mA to 50mA.It indicates that the luminous efficiency decreases more slowly when the high-voltage LED is driven by large current.These results will have a certain reference value for the improvement and optimization of GaN-based high-voltage LEDs.

Study of Structural and Optoelectronic Properties of ZnO Codoped with Ca and Mg

ZnO codoped with Ca and Mg in various proportions was prepared by a chemical method and annealed at 600 C. The structural and optical properties of these oxide samples were systematically studied by XRD, SEM, EDS, and PL spectrometer. XRD pattern shows a hexagonal wurtzite structure. The size of particle as shown by XRD machine and calculated by Scherer’s formula is found in the nano range. The formation of particles showed that they were polycrystalline. Due to larger ionic and covalent radii of Ca than those of Zinc, a lattice deformation occurs with the development of strain field. New phases were observed in XRD pattern of few samples ZnO-2.2 and ZnO-2.4. SEM micrograph shows the formation of nanoparticles. EDS study confirms the codoping of ZnO with Ca and Mg. Optical properties like photoluminescence emission showed a blue shift in peak wavelength. General conductivity and photoconductivity were found high in samples containing certain proportion of Ca and Mg in comparison with pure ZnO.

­Electroluminescent wavelength shift of Si-rich SiO_x based blue and green MOSLEDs induced by O/Si composition Si-QD size variations

Electroluminescent (EL) color shift of Si-rich SiOx with its O/Si composition detuned by changing the RF plasma powers during N2O/SiH4 vapor deposition are investigated. The higher O/Si composition ratio of Si-rich SiOx films when enlarging the RF plasma power contributes to an increment of the insulating SiO2 resistivity and the shrinkage silicon quantum dots (Si-QDs), indicating the fewer injected carriers in Si-QDs. The increasing oxygen content in Si-rich SiOx shortens the diffusion length of Si atoms to constrain the buried Si-QD size. In contrast to the blue-shift of EL peak wavelength induced by enlarging the RF plasma powers, the lengthening deposition time causes a thicker Si-rich SiOx film with more excessive Si atoms, thus providing larger Si-QDs for longer wavelength EL. The EL spectra of metal-oxide-semiconductor light-emitting diodes are red-shifted with increasing the Si-rich SiOx thickness due to the varied Si-QD size and degraded electron conductivity. The uniformity of Si-QDs in Si-rich SiOx layer contributes to the obvious wavelength shift when applying the biased current. The EL peak has a slightly blue-shifted phenomenon when the biased current increases under the band filling effect.

Improved 1.3-$\mu{\rm m}$ Electroluminescence of InGaAs-Capped Type-II GaSb/GaAs Quantum Rings at Room Temperature

Room-temperature 1.3-μm electroluminescence is observed for the InGaAs-capped GaSb quantum rings (QRs). The increasing carrier density in the InGaAs-capped type-II GaSb QRs would induce a larger blue shift in the same laser pumping power span and enhance the luminescence intensity. The enhanced luminescence intensity, a larger blue shift of peak wavelength, and 1.3-μm emission of the InGaAs-capped QR structure have revealed its potential application in multi-wavelength light-emitting devices in the near infrared range.

Step-Roughened N-face GaN Surface on InGaN Light-Emitting Diodes Using a Laser Decomposition Process

InGaN-based light-emitting diodes (LEDs) with a step-inverted pyramidal structure at the GaN/patterned-sapphire interface were fabricated through laser decomposition and wet crystallographic etching processes. By partially reducing the GaN/patterned-sapphire contact area through the step-inverted pyramidal structure, the light output power of the treated LED structure was enhanced 21% compared to a conventional LED structure. By increasing the pulse operation current to 200mA (176 A/cm2), the related efficiency droop and the peak wavelength blueshift phenomenon of the electroluminescence spectrum were almost the same in both LED structures. The light emission intensity at the laser-treated stripe-line region, with the roughened N-face GaN surface, was higher than at the truncated triangle-shaped patterned-sapphire region. LEDs with step-inverted pyramidal structures and GaN/air-gap/patterned-sapphire structures increased light-extraction efficiency for high efficiency nitride-based LEDs.