Efficient 350 nm LEDs on low edge threading dislocation density AlGaN buffer layers
2011
Improving the crystal quality of AlGaN epitaxial layers is essential for the realization of efficient III-nitride-based light
emitting diodes (LEDs) with emission wavelengths below 365 nm. Here, we report on two different approaches to
improve the material quality of AlGaN buffer layers for such UV-LEDs, which are known to be effective for the
MOVPE growth of GaN layers. Firstly, we grew AlGaN on thin GaN nucleation islands which exhibit a threedimensional
facetted structure (3D GaN nucleation). Lateral overgrowth of these islands results in a lateral bending of
dislocation lines at the growing facets. Secondly, in-situ deposited SiN x interlayers have been used as nano-masks
reducing the dislocation density above the SiN x layers. Both approaches result in reduced asymmetric HRXRD ω-scan
peak widths, indicating a reduced edge-type dislocation density. They can be applied to the growth of AlGaN layers with
an Al concentration of at least 20%, thus suitable for LEDs emitting around 350 nm. On-wafer electroluminescence
measurements at 20 mA show an increase in output power by a factor of 7 and 25 for LED structures grown on 3D GaN
nucleation and SiNx interlayer, respectively, compared to structures grown on a purely 2D grown low Al-content AlGaN
nucleation layer. Mesa-LEDs fabricated from the LED layer sequences grown on buffers with SiN x interlayer exhibit a
low forward voltage of 3.8 V at 20 mA and a maximum continuous wave (cw) output power of 12.2 mW at 300 mA.
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