Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten.

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.


Physica status solidi. C 8 (2011), No.7-8, pp.2363-2365
ISSN: 1610-1634
ISSN: 1610-1642
ISSN: 1862-6351
International Workshop on Nitride Semiconductors (IWN) <2010, Tampa/Fla.>
Journal Article, Conference Paper
Fraunhofer IAF ()
AlGaN; dislocation; light emitting diode; photoluminescence; quantum efficiency; UV

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.