Structure and Strain Relaxation of GaN Nanorods Grown on Homoepitaxial Surface via Controlling Irregular Mask

We propose a simple and low-cost approach using irregular mask for growing GaN nanorods (NRs) bottom up on a freestanding GaN substrate through hydride vapor-phase epitaxy. The irregular mask consists of uncoalesced SiO ₂ islands deposited by plasma-enhanced chemical vapor deposition to isolate growth. The selection of the SiO ₂ amount is investigated to achieve reasonable NR density (high coverage), desired morphology (flat side walls and uniform diameters), and lattice quality (single crystalline; better quality than that of an as-grown layer under the same growth ambient). Using this growth approach with appropriate parameters, we successfully synthesize high coverage of uncoalesced NRs on a homoepitaxial surface in a short growth duration. The morphology, density, and growth rate are controlled by adjusting V/III ratios. The cathodoluminescence and photoluminescence measurements of GaN show that luminescence was obtained near 3.4 eV while the structure was grown with mask but contained defect signals when grown without mask. The residual strain relaxation within the GaN NRs has been confirmed using Raman spectrum and scanning transmission electron microscopy strain mapping. Moreover, we demonstrate the strain distribution between different crystalline qualities and lattice orientations in GaN NR. The method provides a quick and inexpensive method for future nanofabrication consideration.