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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. [ABSTRACT FROM AUTHOR]

AlGaN‐based deep‐ultraviolet light‐emitting diodes (DUV LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV LEDs is still much lower than that of blue LEDs due to the quite low light‐extraction efficiency (LEE). We are developing high LEE DUV LEDs by introducing a transparent contact layer and a highly reflective Ni/Al p‐type electrode. In this work, we investigate optimization of the Ni layer thickness of the highly reflective Ni/Al p‐type electrode for AlGaN DUV LEDs. We find that the reflectivity in the UV region becomes higher as the thickness of the Ni layer becomes smaller; however, the external quantum efficiency (EQE) is reduced if the Ni layer is too thin (<0.8 nm). As a result, we find that the most appropriate Ni thickness for the Ni/Al electrode is 0.9 nm. We fabricate 279 nm AlGaN quantum well (QW) DUV LEDs with the optimized electrodes and demonstrate an enhancement in EQE by a factor of 1.8 and a maximum EQE of 9% under bare wafer measurement conditions. We also demonstrate a high output power of 33 mW under an injection current of 100 mA. [ABSTRACT FROM AUTHOR]

AlGaN based deep‐ultraviolet light‐emitting diodes (DUV‐LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV‐LEDs is still much lower than that of blue LEDs due to a quite low light‐extraction efficiency (LEE). We improved the LEE of DUV‐LEDs by using a superlattice (SL) hole spreading p‐AlGaN contact layer, a dot matrix Ni/Au electrode and an Al reflector. DUV‐LED samples in which the SL p‐AlGaN contact layer has various period lengths, and forms two different p‐type electrodes, a conventional Ni/Au electrode and a dot matrix Ni/Au electrode with an Al reflector are fabricated. By comparing these LED samples, it is confirmed that contact layers with relatively longer periods are suitable both for vertical hole injection and lateral spreading of the holes. By increasing the Al content and recovering the transparency of the SL p‐AlGaN contact layer, the LEE is increased by up to a factor of 1.6. [ABSTRACT FROM AUTHOR]

SUMMARY Deep-ultraviolet (DUV) light-emitting diodes (LEDs) are in demand for a wide variety of potential applications, such as sterilization, water and air purification, medical uses, and so on. We have demonstrated 222-351 nm AlGaN and quaternary InAlGaN-based DUV-LEDs by developing a low threading dislocation density (TDD) AlN crystal. We achieved an external quantum efficiency (EQE) of about 4% and an output power greater than 30 mW in DUV-LEDs for use in sterilization applications by developing new crystal growth techniques. [ABSTRACT FROM AUTHOR]

We demonstrated high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs) by improving light-extraction efficiency (LEE) by using a transparent p-AlGaN contact layer and a highly-reflective p-type electrode. We fabricated DUV-LEDs with emission wavelengths between 265-288 nm using p-AlGaN contact layers with compositional wavelength at around 275 nm. The reflectivity of p-type electrode was increased to be approximately 70% by introducing Ni(1nm)/Al layers. The external quantum efficiency (EQE) of the 287 nm LED was increased from 2% to 5.5% by replacing conventional p-GaN contact layer by transparent p-AlGaN contact layer. The increase of LEE was estimated to be by approximately more than 1.7 times. The use of transparent p-AlGaN contact layer is considered to be basic and quite important technique in order to obtain high LEE in DUV LEDs. The EQE of DUV-LED would be much increased by optimizing the device structure and by combining with other approaches to improve LEE. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

High-efficiency ultraviolet (UV) light sources are very attractive for application to the medical field, white lighting, high-density memories, and so on. We have demonstrated that 300- to 370-nm UV emission is considerably enhanced by the introduction of several percent of In into AlGaN due to an In-segregation effect. We fabricated 310-nm-band UV LEDs with quaternary InAlGaN emitting layers on a sapphire substrate and obtained submilliwatt output power. We also fabricated 350-nm-band InAlGaN-based quantum-well LEDs on GaN substrates in order to eliminate the effects of threading dislocations. The maximum UV output power obtained was as high as 7.4 mW under room-temperature CW operation. The maximum external quantum efficiency (EQE) was 1.1% with an injection current of 50 mA, which is the highest EQE ever obtained for 350-nm-band UV LEDs with top-emission geometry. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 43–51, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20287 Copyright © 2006 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The authors demonstrated AlGaN multiquantum-well (MQW) deep-ultraviolet light-emitting diodes (LEDs) with wavelengths in the range of 231–261 nm, fabricated on low threading dislocation density AlN buffers formed through an ammonia (NH3) pulse-flow multilayer growth technique. The authors obtained a single-peaked operation of the AlGaN-MQW LED with a wavelength of 231 nm, which is the shortest wavelength of AlGaN-based LED on sapphire. The maximum output power and external quantum efficiency of the 261 and 231 nm LEDs were 1.65 mW and 0.23% under room-temperature (RT) continuous-wave (cw) operation, and approximately 5 μW and 0.001% under RT pulsed operation, respectively. [ABSTRACT FROM AUTHOR]

Aluminium gallium nitride (AlGaN)‐based ultraviolet‐B light‐emitting diodes (UVB LEDs) are expected to offer smart size, wider choice of UVB light emission in the wavelengths range of 280 nm > λ > 320 nm, and low cost as well as low power consumption compared with other UV light sources including toxic mercury UV‐lamps. The hole‐tunneling from p‐AlGaN side of UVB LED into the multi‐quantum‐wells (MQWs) is strongly dependent on the thickness (TFB) and Al‐contents of undoped (ud)‐AlGaN final barrier (FB). Herein, the photoluminescence (PL) efficiency from MQWs of the UVB LED devices is investigated and compared with the electroluminescence (EL) spectra as a function of TFB. Subsequently, the dependence of PL efficiency, external quantum efficiency (EQE), and light output power on the TFB of UVB LEDs is attempted, using the same growth condition for all samples except variation in TFB. When TFB is set to 6–7 nm, improvements in the EQE and light output power, respectively, from 4.3% and 7 mW to the high values of 5.6% and 17 mW in emission band of 295–300 nm under continuous‐wave (cw) at room temperature (RT) are achieved. [ABSTRACT FROM AUTHOR]

We demonstrated room-temperature (RT) intense ultraviolet (UV) emission in the wavelength range of 315–370 nm from quaternary In[sub x]Al[sub y]Ga[sub 1-x-y]N alloys grown by metalorganic vapor-phase epitaxy. We found that the UV emission is considerably enhanced by the In-segregation effect upon introducing 2%–5% of In into AlGaN. The In incorporation in quaternary In[sub x]Al[sub y]Ga[sub 1-x-y]N is markedly enhanced with the increase of Al content when using a relatively high growth temperature (830–850 °C), resulting in efficient RT UV emission. Maximally efficient emission was obtained at around 330–360 nm from the fabricated quaternary In[sub x]Al[sub y]Ga[sub 1-x-y]N (x=2.0%–4.8%,y=12%–34%). The intensity of the 330 nm emission from quaternary In[sub 0.034]Al[sub 0.12]Ga[sub 0.85]N was as strong as that of the 430 nm emission from In[sub 0.22]Ga[sub 0.78]N at RT. We clearly observed In segregation of submicron size from cathode luminescence images of quaternary InAlGaN films. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrated efficient ultraviolet (UV) photoluminescence (PL) with the wavelength ranging from 230 to 280 nm from Al[sub x]Ga[sub 1-x]N(AlN)/Al[sub y]Ga[sub 1-y]N multiquantum wells (MQWs) grown on SiC by metalorganic vapor phase epitaxy. We systematically investigated the PL intensity of the AlGaN-based MQWs with wide-band-gap AlGaN barriers as functions of QW thickness and Al content of barriers. Single-peak, efficient PL emission was obtained at 282-234 nm at 77 K from Al[sub x]Ga[sub 1-x]N(AlN)/Al[sub y]Ga[sub 1-y]N 5-layer MQWs with approximately 1.5-nm-thick active layers by changing the Al content of the AlxGa[sub 1-x]N barriers from 53% to 100%. The efficiency of the deep-UV emission from AlGaN-based QWs was as high as that of blue emission from InGaN-based QWs at 77 K. [ABSTRACT FROM AUTHOR]