In order to realize 250–350-nm-band high-efficiency deep ultraviolet (UV) emitting devices using group-III-nitride materials, it is necessary to obtain high-efficiency UV emission from wide-band-gap (In)AlGaN. The use of the In-segregation effect, which has already been used for InGaN blue emitting devices, is quite effective for achieving high-efficiency deep UV emission. We have demonstrated high-efficiency UV emission from quaternary InAlGaN-based quantum wells in the wavelength range between 290 and 375 nm at room temperature (RT) using the In-segregation effect. Emission fluctuations in the submicron region due to In segregation were clearly observed for quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15% was estimated for a quaternary InAlGaN-based single quantum well at RT. Such high-efficiency UV emission can even be obtained on high threading-dislocation density buffer layers. A comparison of electroluminescence is made between light-emitting diodes (LEDs) with InAlGaN, AlGaN, and GaN active regions fabricated on SiC substrates with emission wavelengths between 340 and 360 nm. The emission intensity from the quaternary InAlGaN UV-LED was more than one order of magnitude higher than that from the AlGaN or GaN UV-LEDs under RT cw operation. We therefore fabricated 310–350-nm-band deep UV-LEDs with quaternary InAlGaN active regions. We achieved submilliwatt output power under RT pulsed operation for 308–314-nm LEDs. We also demonstrated a high output power of 7.4 mW from a 352-nm quaternary InAlGaN-based LED fabricated on a GaN substrate under RT cw operation. The maximum external quantum efficiency (EQE) of the 352-nm InAlGaN-based LED was higher than that obtained for an AlGaN-based LED with the same geometry. From these results, the advantages of the use of quaternary InAlGaN in 350-nm-band UV emitters were revealed.

Quaternary InAlGaN-based high-efficiency ultraviolet light-emitting diodes

LEDs must be externally driven by power sources to emit light. One problem associated with driving LEDs is its inherent nonlinear relation between the emission intensity and the forward current. Thus, the light output obtained from an LED is strongly dependent on the actual current waveforms employed to drive it. It is found that driving an LED with dc produces light output that surpasses all other techniques including the commonly used pulse-width modulation (PWM) technique. On the other hand, for dimming function, it is found that the PWM technique offers greater dimming flexibility in comparison to dc technique. In this paper, a generalized methodology for driving LEDs inheriting the features of both of these techniques is proposed. It employs a pulsating current switching between two discrete current levels, where the current levels and their durations can be concurrently varied for a more precise mapping of the driving conditions to the light output. The existing dc and PWM techniques can be viewed alternatively as being special cases of this more general approach.

On Driving Techniques for LEDs: Toward a Generalized Methodology

The significant improvements recently achieved in LED technology in terms of lifetime, luminous efficacy, power rating, and color property render LED one of the most promising candidates to replace conventional light sources in various residential and industrial applications. The rapid advancement in the device characteristics has simultaneously stimulated interests in developing efficient LED drivers with optimized control circuitries. The two conventional techniques currently employed in most LED drivers, namely the amplitude-mode and pulsewidth modulation (PWM) mode driving techniques, suffer from the disadvantage that high luminous efficacy in the amplitude mode has to be traded for control flexibility in the PWM mode and vice versa . In this paper, a method is proposed to improve the luminous efficacy of conventional PWM-mode driving technique while retaining their control flexibility by introducing a dc-offset component into the PWM current. Two LEDs were used in the experimental verifications. Improvements of 17.6% and 18.1% on average were measured by maintaining a dc offset of 100 and 200 mA, respectively, in the LED current. Further improvement can be achieved by increasing the dc-offset current. The main tradeoff is the reduction of the dynamic range over which the average LED current can be controlled. For a given set of performance criteria, the proposed method offers designers of LED drivers the flexibility of balancing between luminous efficacy and dynamic range for control.

Bilevel Current Driving Technique for LEDs

An ultraviolet light-emitting diode with peak emission wavelength at 340 nm is reported. The active layers of the device were comprised of quaternary AlInGaN/AlInGaN multiple quantum wells, which were deposited over sapphire substrates using a pulsed atomic-layer epitaxy process that allows precise control of the composition and thickness. A comparative study of devices over sapphire and SiC substrates was done to determine the influence of the epilayer design on the performance parameters and the role of substrate absorption.

/pdf/ultraviolet-light-emitting-diodes-at-340-nm-using-quaternary-29bwj6m70i.pdf

Ultraviolet Light-Emitting Diodes at 340 nm using Quaternary AlInGaN Multiple Quantum Wells

Contributing Authors. Preface. Basic Device Issues in UV Solid-State Emitters and Detectors M.S. Shur, A. Zukauskas. HVPE-Grown AlN-GaN Based Structures for UV Spectral Region A.S. Usikov, et al. GaN-Based Laser Diodes S. Einfeldt, et al. Quaternary AlInGaN Materials System for UV Optoelectronics E. Kuokstis, et al. III-Nitride Based UV Light Emitting Diodes R. Gaska, et al. UV Metal Semiconductor Metal Detectors J.-L. Reverchon, et al. Characterization of Advanced Materials for Optoelectronics by Using UV Lasers and Four-Wave Mixing Techniques K. Jarasiunas. Quantum Phosphors A.P. Vink, et al. Optical Measurements Using Light-Emitting Diodes A. Zukauskas, et al. Novel AlGaN Heterostructures for UV Sensors and LEDs M. Stutzmann. Nitride Photodetectors in UV Biological Effects Studies E. Munoz, et al. Promising Results of Plasma Assisted MBE for Optoelectronic Applications A. Georgakilas, et al. Low Dislocations Density GaN/Sapphire for Optoelectronic Devices B. Beaumont, et al. Stimulated Emission and Gain in GaN Epilayers Grown on Si A.L. Gurskii, et al. Materials Characterization of Group-III Nitrides under High-Power Photoexcitation S. Jursenas, et al. Small Internal Electric Fields in Quaternary InAlGaN Heterostructures S. Anceau, et al. MOCVD Growth of AlGaN Epilayers and AlGaN/GaN SLs in a Wide Composition Range W.V. Lundin, et al. Gallium Nitride Schottky Barriers and MSM UV Detectors B. Boratynski, M. Tlaczala. III-Nitride Based Ultraviolet Surface Acoustic Wave Sensors D. Ciplys, et al. Optically Pumped InGaN/GaN/AlGaN MQW Laser Structures V.Yu. Ivanov, et al. High Power LED and Thermal Management A. Mahlkow. Detection of Blue Light by Self-Assembled Monolayer of Dipolar Molecules O. Nielands, et al. Atomic and Molecular Spectroscopy with UV and Visible Superbright LEDs G. Pichler, et al. Semi-Insulating GaN and its First Tests for RadiationHardness as an Ionizing Radiation Detector J.V. Vaitkus, et al. Towards the Hybrid Biosensors Based on Biocompatible Conducting Polymers A. Ramanaviciene, A. Ramanavicius. Optically Pumped UV-Blue Lasers Based on InGaN/GaN/Al2O3 and InGaN/GaN/Si Heterostructures G.P. Yablonskii, et al. Key Word Index. Author Index.

UV solid-state light emitters and detectors

Operation of InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with quaternary AlInGaN barriers at room and elevated temperatures is reported. The devices outperform conventional GaN/InGaN MQW LEDs, especially at high pump currents. From the measurements of quantum efficiency and total emitted power under dc and pulsed pumping, we show the emission mechanism for quaternary barrier MQWs to be predominantly linked to band-to-band transitions. This is in contrast to localized state emission observed for conventional InGaN/InGaN and GaN/InGaN LEDs. The band-to-band recombination with an increased quantum-well depth improves the high-current performance of the quaternary barrier MQW LEDs, making them attractive for high-power solid-state lighting applications.

/pdf/band-edge-luminescence-in-quaternary-alingan-light-emitting-4hut541uve.pdf

Band-edge luminescence in quaternary AlInGaN light-emitting diodes

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Band-edge luminescence in quaternary AlInGaN light-emitting diodes