Investigation of anisotropic wafer bending curvature in a-plane GaN films grown on r-plane sapphire substrates

We grew GaN films on r -plane sapphire substrates by pulsed sputtering and investigated their structural properties. X-ray diffraction measurements revealed that a-plane GaN grows epitaxially on r-plane sapphire with an epitaxial relation of [0001] GaN // [ 1 ¯ 101 ] sapphire and [ 1 ¯ 101 ] GaN // [ 11 2 ¯ 0 ] sapphire . In situ wafer curvature measurements revealed that the anisotropic compressive strain along [ 1 1 ¯ 00 ] and [0001] GaN is generated during the initial stage of growth as a consequence of the anisotropy in the lattice mismatch between a -plane GaN and r -plane sapphire. We also observed that the coalescence of the GaN islands can lead to a change of stresses from compressive to tensile.