Etching of the SiGa_xN _yPassivation Layer for Full Emissive Lateral Facet Coverage in InGaN/GaN Core-Shell Nanowires by MOVPE

To strongly enhance the vertical growth rate in MOVPE-grown GaN core-shell wires, large quantities of silane (SiH4) need to be introduced for the growth of the wire core. This results in the formation of a SiGaxNy layer that acts effectively as a dielectric mask on the sidewalls of the GaN core, thereby promoting vertical growth. While its presence is useful during core growth, it precludes the formation of homogeneous core-shell heterostructures, whose coverage and optical quality tend to be maximized at the top of the wires. In this paper, we propose three different strategies to remove this passivating layer once its initial role is accomplished. They are based on chemical, physical, or thermal etching. Their effects on the optical quality of subsequent core-shell InGaN/GaN heterostructures, including single and multiple-quantum-well heterostructures, have been analyzed. Overall, an ex situ chemical etching of SiGaxNy by H3PO4 results in an enhanced emissive coverage and a stronger overall luminescence intensity from the active regions, while simultaneously removing deep-defect emissions arising from the high growth temperature of the core.