Analysis of HVPE grown AlGaN layers on honeycomb patterned sapphire

• HVPE grown AlGaN layers on patterned sapphire substrates were analyzed. XRD was used to determine three different orientations of AlGaN in the layers
• EBSD was used to determine protruding crystallites which hinder c-plane layer coalescence.
• All crystallites found with XRD texture analysis could be found and addressed with EBSD and cross-sectional SEM. Two orientations were addressed to be already published (11–22) and (1–103) AlGaN nucleating on m-plane sapphire sidewalls.
• Protruding crystallites which hinder layer coalescence is proposed to be c-plane AlGaN on n-plane sapphire according to schematic.

Thick AlxGa1−xN layers were grown by hydride vapor phase epitaxy on hexagonally patterned sapphire substrates. Non-c-planar growth is found inside the etched honeycombs which in part hinders coalescence of the c-plane AlGaN layer growing on top of the ridges. From X-ray diffraction, electron backscatter diffraction and scanning electron microscopy, the orientations of the parasitic crystallites were identified as {11–22} and {1–103} AlGaN growing on m-plane sapphire sidewalls as well as c-plane oriented AlGaN growing on n-plane sidewall facets which are located in the corners of the combs. According to the geometry of parasitic crystallites, it is further observed, that the semipolar growth occurring on sapphire m-plane sidewalls does not hinder the coalescence of c-plane AlGaN growing on top of the ridges, whereas fast propagation of parasitic crystallites nucleating on n-plane sidewall facets leads to delayed layer coalescence.