A comparative study on the properties of c-plane and a-plane GaN epitaxial films grown on sapphire substrates by pulsed laser deposition

Abstract

∼500 nm-thick c-plane and a-plane GaN epitaxial films on c-plane and r-plane sapphire substrates by pulsed laser deposition have been grown and explored. The ∼500 nm-thick c-plane GaN epitaxial films grown on c-plane sapphire substrates show high crystalline quality with full-width at half-maximum (FWHM) for GaN(0002) and GaN(10–12) X-ray rocking curves (XRCs) of 0.20° and 0.37°, respectively, very smooth GaN surface with a root-mean-square (RMS) surface roughness of 1.4 nm, sharp and abrupt c-plane GaN/c-plane sapphire hetero-interfaces, a −0.116 GPa residual stress, and high optical property. These results are in striking contrast to those of ∼500 nm-thick a-plane GaN epitaxial films grown on r-plane sapphire substrates. The ∼500 nm-thick a-plane GaN epitaxial films grown on r-plane sapphire substrates show poor crystalline quality with FWHM for GaN(11–20) and GaN(10–11) XRC of 0.72° and 0.81°, respectively, rough GaN surface with an RMS surface roughness of 7.2 nm, indistinct a-plane GaN/r-plane sapphire hetero-interface with a ∼1.5 nm-thick interfacial layer, a −0.884 GPa residual stress, and poor optical property. This work brings further insight into fully understanding of the properties of GaN epitaxial films grown on c-plane and r-plane sapphire substrates for obtaining high-quality GaN epitaxial films in the application of GaN-based devices.