Atom Probe Tomography Analysis of Gallium-Nitride-Based Light-Emitting Diodes

Thin-film light-emitting diodes (LEDs) composed of GaN/In$_{x}$Ga$_{1-x}$N/GaN quantum well (QW) structures are integrated into modern optoelectronic devices because of the tunable InGaN band-gap enabling emission of the full visible spectrum. Atom probe tomography (APT) offers unique capabilities for 3D device characterization including compositional mapping of nano-volumes (\textgreater 10$^{6}$ nm$^{3})$, high detection efficiency (\textgreater 50{\%}), and good sensitivity [1]. In this study, APT is used to understand the distribution of dopants as well as Al and In alloying agents in a GaN device. Measurements using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) have also been made to improve the accuracy of the APT analysis by correlating the information content of these complimentary techniques. APT analysis reveals various QW and other optoelectronic structures including a Mg p-GaN layer, an Al-rich electron blocking layer, an In-rich multi-QW region, and an In-based super-lattice structure. The multi-QW composition shows good quantitative agreement with layer thickness and spacing extracted from a high resolution TEM image intensity analysis. [1] T. F. Kelly and D. J. Larson, Annual Reviews of Materials Research 42 (2012) 1.