scholarly journals Improved Performance of GaN-Based Ultraviolet LEDs with the Stair-like Si-Doping n-GaN Structure

Crystals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1203
Author(s):  
Xiaomeng Fan ◽  
Shengrui Xu ◽  
Hongchang Tao ◽  
Ruoshi Peng ◽  
Jinjuan Du ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Light Output ◽  
Current Crowding ◽  
X Ray Diffraction ◽  
Light Emitting ◽  
Si Doping ◽  
Uv Led ◽  
Wall Plug Efficiency ◽  
Improved Performance ◽  
Uv Leds

A method to improve the performance of ultraviolet light-emitting diodes (UV-LEDs) with stair-like Si-doping GaN layer is investigated. The high-resolution X-ray diffraction shows that the UV-LED with stair-like Si-doping GaN layer possesses better quality and a lower dislocation density. In addition, the experimental results demonstrate that light output power and wall plug efficiency of UV-LED with stair-like Si-doping GaN are significantly improved. Through the analysis of the experimental and simulation results, we can infer that there are two reasons for the improvement of photoelectric characteristics: reduction of dislocation density and alleviating of current crowding of UV-LEDs by introduced stair-like Si-doping GaN.

scholarly journals A 3 W High-Voltage Single-Chip Green Light-Emitting Diode with Multiple-Cells Network

2015 ◽  
Vol 2015 ◽  
pp. 1-4 ◽  
Author(s):  
W. Wang ◽  
Y. Cai ◽  
Y. B. Zhang ◽  
H. J. Huang ◽  
W. Huang ◽  
...  
Keyword(s):  
High Voltage ◽  
Light Emitting Diode ◽  
Light Output ◽  
Green Light ◽  
Current Crowding ◽  
Single Chip ◽  
Light Output Power ◽  
Large Area ◽  
Light Emitting ◽  
Multiple Cells

A parallel and series network structure was introduced into the design of the high-voltage single-chip (HV-SC) light-emitting diode to inhibit the effect of current crowding and to improve the yield. Using such a design, a6.6×5 mm2large area LED chip of 24 parallel stages was demonstrated with 3 W light output power (LOP) at the current of 500 mA. The forward voltage was measured to be 83 V with the same current injection, corresponding to 3.5 V for a single stage. The LED chip’s average thermal resistance was identified to be 0.28 K/W by using infrared thermography analysis.

Defect controls by silicon doping in non-polar a-plane AlGaN epi-layers

2021 ◽  
Vol 11 (9) ◽  
pp. 1466-1475
Author(s):  
Tianlong He ◽  
Ming Tian ◽  
Junhua Yin ◽  
Shuai Chen ◽  
Lingyu Wan ◽  
...  
Keyword(s):  
Shallow Donor ◽  
Structural Defects ◽  
Silicon Doping ◽  
Light Emitting ◽  
Si Doping ◽  
Carrier Recombination ◽  
Line Defects ◽  
Si Doped ◽  
Donor States ◽  
Uv Leds

Deposition of high-quality Si-doped crystalline AlGaN layers, especially non-polar-grown AlGaN layers, is critical and remains difficult in preparing AlGaN-based light-emitting diodes (LEDs), as the Si-doping-induced variations of crystalline structures are still under exploration. In this work, structural characterizations of Si-doped AlxGa1−xN layers were carried out by associating with examination of their carrier recombination behaviors in photoluminescence (PL) processes, to clarify the physical mechanism on how Si doping controls the formation of structural defects in AlGaN alloy. The obtained results showed that Si doping induced extrinsic shallow donor states and increased the densities of point defects like cation vacancies. On the contrary, Si doping suppressed formation of line defects like dislocations and planar defects like stacking faults with suitable doping concentration. These results may guide further improvement of UV-LEDs based on AlGaN alloy.

ACCURATE MEASUREMENT OF ULTRAVIOLET LIGHT-EMITTING DIODES

2021 ◽  
Author(s):  
C. Yuqin Zong ◽  
Cameron Miller
Keyword(s):  
Ultraviolet Light ◽  
Light Emitting Diodes ◽  
Luminous Flux ◽  
Junction Temperature ◽  
Integrating Sphere ◽  
Light Emitting ◽  
Type D ◽  
Uv Led ◽  
Uv Leds ◽  
Ultraviolet Light Emitting Diodes

We have developed a new calibration capability for 200 nm to 400 nm ultraviolet light-emitting diodes (UV LEDs) using a Type D gonio-spectroradiometer. The recently-introduced mean differential continuous pulse (M-DCP) method is used to overcome the measurement difficulty associated with the initial forward voltage, VF, anomaly of a UV LED, which makes it impossible to use VF to infer junction temperature, TJ, during pulsed operation. The new measurement facility was validated indirectly by comparing the measured total luminous flux of a white LED with that measured using the NIST’s 2.5 m absolute integrating sphere. The expanded calibration uncertainty for the total radiant flux is approximately 2 % to 3 % (k = 2) depending the wavelength of the UV LED.

scholarly journals 3D Microlithography Using an Integrated System of 5-mm UV-LEDs with a Tilt-Rotational Sample Holder

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 157 ◽  
Author(s):  
Sabera Fahmida Shiba ◽  
Hyeongmin Jeon ◽  
Jong-Soo Kim ◽  
Jong-Eun Kim ◽  
Jungkwun Kim
Keyword(s):  
Light Source ◽  
Light Emitting Diode ◽  
Vertical Direction ◽  
Ultra Violet ◽  
Integrated System ◽  
Sample Holder ◽  
Large Area ◽  
Light Emitting ◽  
Uv Led ◽  
Uv Leds

This paper demonstrates a 3D microlithography system where an array of 5 mm Ultra Violet-Light Emitting Diode (UV-LED) acts as a light source. The unit of the light source is a UV-LED, which comes with a length of about 8.9 mm and a diameter of 5 mm. The whole light source comprises 20 × 20 matrix of such 5 mm UV-LEDs giving a total number of 400 LEDs which makes it a very favorable source with a large area for having a batch production of the desired microstructures. This light source is able to give a level of precision in microfabrication which cannot be obtained using commercial 3D printers. The whole light source performs continuous rotational movement once it is turned on. This can also move up and down in a vertical direction. This multidirectional light source also comprises a multidirectional sample holder. The light source teaming up with the multidirectional sample holder highly facilitates the process of fabrication of a huge range of 3D structures. This article also describes the different levels of characterization of the system and demonstrates several fabricated 3D microstructures including high aspect ratio vertical micro towers, twisted turbine structures, triangles, inclined pillar ‘V’ structures, and hollow horn structures as well.

scholarly journals Transcriptome and metabolome analyses revealed that narrowband 280 and 310 nm UV-B induce distinctive responses in Arabidopsis

2021 ◽  
Author(s):  
Tomohiro Tsurumoto ◽  
Yasuo Fujikawa ◽  
Daisaku Ohta ◽  
Atsushi Okazawa
Keyword(s):  
Anthocyanin Biosynthesis ◽  
Uv Light ◽  
Current Model ◽  
Phenylpropanoid Pathway ◽  
Metabolic Responses ◽  
Uv Resistance ◽  
Light Emitting ◽  
Uv Led ◽  
Uv Leds ◽  
Led Irradiation

SUMMARYIn plants, the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8) perceives UV-B and induces UV-B responses including synthesis of UV-B absorbing phenolic compounds such as anthocyanins. UVR8 absorbs a range of UV-B (260–335 nm). However, the responsiveness of plants to each UV-B wavelength has not been intensively studied so far. Here, we performed transcriptome and metabolome analyses of Arabidopsis using UV light emitting diodes (LEDs) with peak wavelengths of 280 and 310 nm to investigate the differences in the wavelength-specific UV-B responses. Irradiation with both UV-LEDs induced gene expression of the transcription factor ELONGATED HYPOCOTYL 5 (HY5), which has a central role in the UVR8 signaling pathway. However, the overall transcriptomic and metabolic responses to 280 and 310 nm UV-LED irradiation were different. Most of the known UV-B-responsive genes, such as salicylic acid, jasmonic acid, and defense-related genes, responded only to 280 nm UV-LED irradiation. Lipids, polyamines and organic acids were the metabolites most affected by 280 nm UV-LED irradiation, whereas the effect of 310 nm UV-LED irradiation on the metabolome was considerably less. Enzymatic genes involved in the phenylpropanoid pathway upstream in anthocyanin biosynthesis were up-regulated only by 280 nm UV-LED irradiation. On the other hand, no enzymatic genes downstream in anthocyanin biosynthesis were induced by the UV-LEDs, but rather, they were down-regulated by 310 nm UV-LED irradiation. These results revealed that the responsivenesses of Arabidopsis to 280 and 310 nm UV-B were significantly different, suggesting that UV-B signaling is mediated by more complex pathways than the current model.

Comparison of the Electroluminescence of Blue and Deep-UV Light-Emitting Diodes at Elevated Temperatures

2005 ◽  
Vol 892 ◽  
Author(s):  
Xian-An Cao ◽  
T. Stecher ◽  
S. LeBoeuf
Keyword(s):  
Light Emitting Diodes ◽  
Elevated Temperatures ◽  
Characteristic Temperature ◽  
Light Output ◽  
Band Edge Emission ◽  
Light Emitting ◽  
Blue Led ◽  
Uv Led ◽  
Dominant Band ◽  
Deep Uv

AbstractThe performance of InGaN and AlGaN-based blue (465nm) and deep ultraviolet (UV) (280 nm) light-emitting diodes (LEDs) at elevated temperatures (25-175 °C) were investigated. As a result of uniform high-Al content AlGaN alloys yielded by migration-enhanced metalorganic chemical vapor deposition, the deep-UV LED showed dominant band-edge emission, much smaller alloy broadening and weaker localization effects as compared to the InGaN LED. Strong carrier localization was retained in the blue LED up to 175 °C, leading to temperature-independent emission intensity at low-energy tails. The UV LED, however, showed a much more rapid decrease in light output with increasing temperature. The characteristic temperature was 37 K, compared to 270 K for the blue LED. These findings implicate the lack of localization effects in AlGaN alloys as one of the causal factors in the poor thermal performance of the deep UV LED and suggest that increasing carrier confining potentials will provide a critical means to improve its thermal stability.

Deep Ultraviolet Light Emitting Diodes with Emission below 300 nm

2005 ◽  
Vol 892 ◽  
Author(s):  
M. Asif Khan
Keyword(s):  
Multiple Quantum Well ◽  
Structure Design ◽  
Multiple Quantum ◽  
Device Structure ◽  
Light Emitting ◽  
Uv Led ◽  
Excellent Research ◽  
Deep Uv ◽  
P Type ◽  
Uv Leds

AbstractIn this paper we will describe the problems in growth and fabrication of deep UV LED devices and the approaches that we have used to grow AlGaN-based multiple quantum well deep UV LED structures and to overcome issues of doping efficiency, cracking, and slow growth rates both for the n- and the p-type layers of the device structures. Several innovations in structure growth, device structure design and fabrication and packaging have led to the fabrication of devices with emission from 250-300 nm and cw-milliwatt powers at pump currents of only 20 mA (Vf ≤ 6 V). Record wall plug efficiencies above 1.5 % are now achievable for devices with emission at 280 nm. Thermal management and a proper device design are not only key factors in achieving these record performance numbers but are also crucial to device reliability. We will also discuss some of our initial research to clarify the factors influencing the lifetime of the deep UV LEDs. In addition to our own work, we will review the results from the excellent research carried out at several other laboratories worldwide.

scholarly journals Light-Output Enhancement of GaN-Based Light-Emitting Diodes with Three-Dimensional Backside Reflectors Patterned by Microscale Cone Array

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Huamao Huang ◽  
Jinyong Hu ◽  
Hong Wang
Keyword(s):  
Light Emitting Diode ◽  
Three Dimensional ◽  
Light Output ◽  
Bragg Reflector ◽  
Light Extraction Efficiency ◽  
Distributed Bragg Reflector ◽  
Etching Technique ◽  
Light Emitting ◽  
Triangle Lattice ◽  
Wall Plug Efficiency

Three-dimensional (3D) backside reflector, compared with flat reflectors, can improve the probability of finding the escape cone for reflecting lights and thus enhance the light-extraction efficiency (LEE) for GaN-based light-emitting diode (LED) chips. A triangle-lattice of microscale SiO2cone array followed by a 16-pair Ti3O5/SiO2distributed Bragg reflector (16-DBR) was proposed to be attached on the backside of sapphire substrate, and the light-output enhancement was demonstrated by numerical simulation and experiments. The LED chips with flat reflectors or 3D reflectors were simulated using Monte Carlo ray tracing method. It is shown that the LEE increases as the reflectivity of backside reflector increases, and the light-output can be significantly improved by 3D reflectors compared to flat counterparts. It can also be observed that the LEE decreases as the refractive index of the cone material increases. The 3D 16-DBR patterned by microscale SiO2cone array benefits large enhancement of LEE. This microscale pattern was prepared by standard photolithography and wet-etching technique. Measurement results show that the 3D 16-DBR can provide 12.1% enhancement of wall-plug efficiency, which is consistent with the simulated value of 11.73% for the enhancement of LEE.

scholarly journals Simulation of an Improved Design for n-Electrode with Holes for Thin-GaN Light-Emitting Diodes

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Farn-Shiun Hwu
Keyword(s):  
Light Emitting Diodes ◽  
Three Dimensional ◽  
Light Output ◽  
Electrical Characteristics ◽  
Light Emitting ◽  
Temperature Distributions ◽  
Gan Led ◽  
Wall Plug Efficiency ◽  
Improved Design ◽  
Novel Design

A novel design is proposed for n-electrode with holes to be applied in Thin-GaN light-emitting diodes (LEDs). The influence of the n-electrode with holes on the thermal and electrical characteristics of a Thin-GaN LED chip is investigated using a three-dimensional numerical simulation. The variations in current density and temperature distributions in the active layer of n-electrodes both with and without holes are very tiny. The percentages of light output from these holes are 29.8% and 38.5% for cases with 5 μm holes and 10 μm holes, respectively; the side length of the n-electrode (L) is 200 μm. Furthermore, the percentage increases with the size of the n-electrode. Thus, the light output can be increased 2.45 times using the n-electrode with holes design. The wall-plug efficiency (WPE) can also be improved from 2.3% to 5.7%. The most appropriate n-electrode and hole sizes are determined by WPE analysis.

scholarly journals Improving Emission Uniformity of InGaN/GaN-Based Vertical LEDs by Using Reflective ITO/Ag n-Contact

Electronics ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 975
Author(s):  
Woong-Sun Yum ◽  
Ji-Hyun Koo ◽  
Dae-Hee Lee ◽  
Young-Hoon Kim ◽  
Young-Kyu Jeong ◽  
...  
Keyword(s):  
Output Power ◽  
Light Emitting Diodes ◽  
Reference Sample ◽  
Light Output ◽  
Light Output Power ◽  
Forward Voltage ◽  
Light Emitting ◽  
Wall Plug Efficiency ◽  
Chip Size ◽  
Reference Samples

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.

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