Effect of residual stress on the microstructure of GaN epitaxial films grown by pulsed laser deposition

The stress-free GaN epitaxial films have been directly grown by pulsed laser deposition (PLD) without any interlayer, and the effect of different stress on the microstructure of as-grown GaN epitaxial films has been explored in detail. The as-grown stress-free GaN epitaxial films of ∼320 nm-thick exhibit very smooth surface without any particles and grains with the root-mean-square surface roughness of 2.3 nm measured by atomic force microscopy. The relatively high crystalline quality is confirmed by the smaller full-width at half maximum values of GaN(0002) and GaN(101¯2) X-ray rocking curves as 0.27° and 0.68°, respectively.