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Improved quantum efficiency of 350 nm LEDs grown on low dislocation density AlGaN buffer layers

 
: Kunzer, M.; Gutt, R.; Kirste, L.; Passow, T.; Forghani, K.; Scholz, F.; Köhler, K.; Wagner, J.

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Physica status solidi. C 8 (2011), Nr.7-8, S.2363-2365
ISSN: 1610-1634
ISSN: 1610-1642
ISSN: 1862-6351
International Workshop on Nitride Semiconductors (IWN) <2010, Tampa/Fla.>
Englisch
Zeitschriftenaufsatz, Konferenzbeitrag
Fraunhofer IAF ()
AlGaN; dislocation; light emitting diode; photoluminescence; quantum efficiency; UV

Abstract
The effect of buffer layers with reduced defect density on the efficiency of AlGaN based UV LED structures has been investigated. We report on two approaches of defect reduction: Firstly, AlGaN was grown on thin GaN nucleation islands which exhibit a three-dimensional facetted structure (3D nucleation). Secondly, AlGaN buffer layers with in-situ SiNx nano-masking interlayers inserted were employed. Both approaches result in reduced widths of asymmetric high-resolution X-ray diffraction w-scan peaks. Full LED structures were grown on these buffer layers and are compared to structures grown on a purely 2D grown low Al-content AlGaN nucleation layer. The influence of the different buffer layer technologies, and hence defect density, on the quantum efficiency has been investigated by excitation-density and temperature dependent photoluminescence. The data indicate an increase in the PL efficiency from below 5% for 2D nucleation to 15% for 3D nucleation and up to 50% for structures grown on SiNx interlayer buffers. These results are in line with electroluminescence measurements taken on-wafer. The output power at 40 mA emitted through the substrate for the 3D nucleated LED structure is 0.3 mW which corresponds to an increase by a factor of 9 compared to similar LED structures grown in 2D mode. The same LED structure grown on an AlGaN buffer containing SiNx interlayers showed a 30× enhancement in efficiency with an output power of 0.51 mW at 20 mA, rising linearly to 1.05 mW for a current of 40 mA.

: http://publica.fraunhofer.de/dokumente/N-180348.html