MOCVD growth of GaN films onSi-rich SiN_x, nanoislands patterned sapphire

摘要

We intentionally patterned Si-rich SiN_x nanoislands on sapphire substrates and found the SiN_x significantly influenced the subsequent growth of GaN films. Distinct GaN islands of triangular base were formed caused by the enhanced diffusion and regrowth anisotropy during the annealing processes of GaN nucleation layers. Subsequent growth of GaN epilayers at high temperature with initial low V/III ratios on the nucleated triangular islands resulted in island coarsening and shape variations from triangular to hexagonal due to the dominating gas phase transport growth mechanism and limited diffusion length. Further growth with high V/III ratios eventually resulted in layer-growth with surface roughness of –2.6 A. Both AFM and XRD results showed a significant improvement of the crystalline qualities with estimated threading dislocation (TD) density of about 1 x 10~8 cm~(-2) when Si-rich SiN_x nanoislands patterning was performed. Photoluminescence measurements showed that the yellow and blue emissions were substantially suppressed.