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Kim Y.S.,Rensselaer Polytechnic Institute | Lin S.-Y.,Rensselaer Polytechnic Institute | Hsieh M.-L.,National Taiwan Normal University | Schowalter L.,Crystal IS Inc.
2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011 | Year: 2011

Ultra-violet light-emitting diodes (UV-LEDs) fabricated with integrated surface textures show an enhancement of the output power and more directionality of the emitted light, which is in agreement with the calculated results. © 2011 OSA.

Sampath A.V.,U.S. Army | Garrett G.A.,U.S. Army | Readinger E.D.,U.S. Army | Enck R.W.,U.S. Army | And 4 more authors.
Solid-State Electronics | Year: 2010

The optical and structural properties of AlGaN active regions containing nanoscale compositional inhomogeneities (NCI) grown on low dislocation density bulk AlN substrates are reported. These substrates are found to improve the internal quantum efficiency and structural quality of NCI-AlGaN active regions for high Al content alloys, as well as the interfaces of the NCI with the surrounding wider bandgap matrix, as manifested in the absence of any significant long decay component of the low temperature radiative lifetime, which is well characterized by a single exponential photoluminescence decay with a 330 ps time constant. However, room temperature results indicate that non-radiative recombination associated with the high point defect density becomes a limiting factor in these films even at low dislocation densities for larger AlN mole fractions. © 2010 Elsevier Ltd. All rights reserved.

Garrett G.A.,U.S. Army | Sampath A.V.,U.S. Army | Shen H.,U.S. Army | Wraback M.,U.S. Army | And 10 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2010

Temperature dependent time-resolved photoluminescence is used to study the development of active regions for optoelectronic devices employing AlGaN nanostructures for deep-UV emission. The changing importance of dislocation versus point defects and their relationship to different forms of carrier localization are discussed. The results presented suggest that AlGaN nanostructure development for deep-UV emitters require both point defect/impurity suppression for improved efficiency and lower dislocation density for improved interface quality. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Grandusky J.R.,Crystal IS Inc. | Gibb S.R.,Crystal IS Inc. | Mendrick M.C.,Crystal IS Inc. | Schowalter L.J.,Crystal IS Inc.
Applied Physics Express | Year: 2010

High quality bulk aluminum nitride substrates were used to obtain pseudomorphic AlxGa1-xN layers with low dislocation density, smooth surfaces, and high conductivity. These layers were fabricated into mid-ultraviolet light emitting diodes with peak wavelengths in the range of 240-260 nm. The low dislocation density of the pseudomorphic quantum wells resulted in improved performance over previously published data. The output powers of the on-wafer measurements were greater than 5mW in continuous wave operation, and 16mW in pulsed operation. This was achieved utilizing single die (with an active area of 1 x 10-3 cm2). © 2010 The Japan Society of Applied Physics.

Gibb S.R.,Crystal IS Inc. | Grandusky J.R.,Crystal IS Inc. | Mendrick M.,Crystal IS Inc. | Schowalter L.J.,Crystal IS Inc.
International Journal of High Speed Electronics and Systems | Year: 2011

Low dislocation density pseudomorphic epitaxial layers of Al xGa 1-xN have been grown on c-face AlN substrates prepared from high quality bulk crystals. As reported previously, pseudomorphic growth yields very low dislocation density layers with atomically smooth surfaces throughout the active region of a full LED device structure. An advantage of the low dislocation density is the ability to n-type dope the high aluminum content Al xGa 1-xN (x ∼ 70%) epitaxial layers required for UVLED devices to obtain sheet resistances less than 350 Ohm/square for 0.5 μm thick layers. Here, we report on the characterization of our pseudomorphic epitaxial AlGaN layers via cathodoluminescence (CL) and on-wafer and initial packaged level characterization of fully fabricated pseudomorphic ultraviolet LEDs (PUVLEDs) with an emission wavelength between 250 - 265 nm. An additional benefit of PUVLED devices is the ability to run these devices at high input powers and current densities. Further, the aforementioned low dislocation density of the epitaxial structure results in improved device performance over previously published data. Mean output powers of greater than 4 mW were obtained on-wafer prior to thinning and roughening while output powers as high as 45 mW were achieved for packaged devices. © 2011 World Scientific Publishing Company.

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