Using nanoindentation and cathodoluminescence to identify the bundled effect of gallium nitride grown by PA-MBE

Abstract

We performed cathodoluminescence (CL) investigations on GaN NCs grown using molecular beam epitaxy. Bundled GaN was used to form NCs that were deposited onto commercial sapphire templates. The structures of the bundled NCs were analyzed using nanoindentation. The samples were grown with a TG of 700, 800, and 850 °C, and the H values were 7.4 ± 0.2 and 6.4 ± 0.2 GPa; the E values were 308.4 ± 4.3, 296.4 ± 3.8, and 75.5 ± 1.4 GPa, respectively. It is suspected that the discrepancies of the mechanical parameters obtained by various indentation methods are partially a result of the stress distribution inherent in the different orientations on the sapphire substrate.A scanning electron microscopy (SEM) system equipped with CL allows the direct comparison of SEM images and CL maps, captured from exactly the same area of the samples. In addition to the SEM and CL images, photoluminescence spectroscopy (PL) profiling was obtained by collecting the 20 K PL spectra at the samples. The PL profiling enables the distinguishing of the emissions by the 5 meV of the blueshift from 3.440 to 3.445 eV due to localization effects. The bundled GaN NCs resulted from the (0002) reflection at 34.6° for a wurtzite structure and a raised intensity difference when the TG was increased from 700 to 850 °C. The crystal texture of the GaN can influence the mechanical properties at different TG stages.