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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]

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]

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]