Depth-dependent strain distribution in AlGaN-based deep ultraviolet light-emitting diodes using surface-plasmon-enhanced Raman spectroscopy

Ex situ depth-dependent strain distribution in AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) was investigated through surface-plasmon-enhanced Raman spectroscopy with an optimally truncated structure. In this study, the strain was selectively analyzed by an ex situ method as a function of the distance from the sapphire substrate followed by AlN relaxation layers. Experimental results for DUV LEDs with a complex structure showed that the strain was non-uniformly distributed with the thickness and that the compressive strain tended to gradually decrease when the AlGaN layer or the AlN relaxation layer was grown from the substrate. We quantitatively determined the subtle changes in the additional strain caused by the lattice mismatch between the underlying layers subjected to the residual compressive strain.