Using Cross-Sectional Cathodoluminescence to Visualize Process-Induced Defects in GaN-Based High Electron Mobility Transistors
We performed cross-sectional cathodoluminescence (CL) for gallium nitride (GaN)-based high electron mobility transistors (HEMTs) to investigate process-induced defects. The cross-sectional CL measurements at room temperature clearly show the intensity distribution for the 25 nm-thick AlGaN layer, even though it is very thin. We also observed that the intensities of the band-edge emissions from the AlGaN and GaN layers fall near the source and drain regions. Those intensity decays demonstrate that ion implantation at the source and drain regions generates many nonradiative recombination centers and that these defects are not eliminated even by activation annealing after ion implantation. We also observed that the intensity of yellow luminescence (YL) in the GaN layer drops not only at the source and drain regions, but also in deeper regions of the 1.4 μm-thick GaN layer. We consider diffusion of the implantation-generated defects and their interactions with point defects in this deep region, which are responsible for the YL, to be the mechanism responsible for the YL intensity decrease. Ion implantation and subsequent annealing not only activates the dopant atoms, but also changes the point defects, which may affect the device characteristics. These findings show that cross-sectional CL spectral mapping can visualize the process-induced defects in GaN HEMTs and can therefore be used for process optimization and failure analysis of these devices.