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In this work, we demonstrate that depth-resolved confocal micro-Raman spectroscopy can be used to characterize the active layer of GaN-based LEDs. By taking the depth compression effect due to refraction index mismatch into account, the axial profiles of Raman peak intensities from the GaN capping layer toward the sapphire substrate can correctly match the LED structural dimension and allow the identification of unique Raman feature originated from the 0.3 μm thick active layer of the studied LED. The strain variation in different sample depths can also be quantified by measuring the Raman shift of GaN A1(LO) and E2(high) phonon peaks. The capability of identifying the phonon structure of buried LED active layer and depth-resolving the strain distribution of LED structure makes this technique a potential optical and remote tool for in operando investigation of the electronic and structural properties of nitride-based LEDs.

We study the basal plane stacking faults (BSFs) related optical properties in a-plane AlGaN alloys with different Al composition ranging from 0 to 0.28. The low-temperature photoluminescence (PL) spectra for AlGaN show two dominant peaks attributed to the emission of near band edge and BSFs-bound excitons, respectively. The PL integrated intensity ratio of the BSFs to NBE is found to correlate to the density of BSFs observed by the transmission electron microscopy. Finally, the exciton localization behaviors of BSFs in a-plane AlGaN alloys is observed and discussed in this study.

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