AlN Buffer Enhances the Layer Quality of MBE-Grown Cubic GaN on 3C-SiC

Cubic nitrides are candidate materials for next-generation optoelectronic applications as they possess no internal fields and promise to cover large parts of the electromagnetic spectrum from the deep UV toward the mid-infrared. Their successful application demands high-quality epitaxial growth of c-GaN as a base material. This infers a virtually perfect crystallinity as well as smooth surfaces and interfaces despite the limited availability of suitable substrate materials. Here, we systematically introduce pre-growth treatments and c-AlN buffer layers to optimize c-GaN epitaxial layers. Optimized growth parameters yield extremely small surface roughness values below 1 nm root mean square of phase pure c-GaN layers with very limited stacking fault densities as highlighted by scanning transmission electron microscopy. The crystallinity is monitored by X-ray diffraction and surpasses the current standards. We study the effects of the pre-growth procedures on the optical response by photoluminescence spectroscopy and reconfirm the high structural quality of the epitaxial layers. The combined optimization of all layer properties through the universally applicable approach allows for the growth of more complex quantum structures toward device applications.