Anisotropic X-ray Rocking Curve Due to a Damaged Surface Layer in a Freestanding GaN Thick Film

다국어 초록 (Multilingual Abstract)

The structural deformation of freestanding GaN film has been investigated. The specimen was
grown on an Al2O3 substrate by using hydride vapor phase epitaxy (HVPE) and was self-detached
during the growth. the atomic force microscopy (AFM) image showed much mechanical damages
on the surface, which was presumably generated by the surface polishing process. After chemical
etching, the near-band-edge to yellow-band (NBE/YB) luminescence intensity ratio was greatly
increased. Also, using high resolution X-ray diraction (HRXRD), we found that the 2-! scan
of (0002) reflection asymmetrically broadened at low diraction angles, which indicated that a
damaged surface layer existed in the film with residual compressive strain. Moreover, a more
detailed X-ray analysis showed that the surface had a concave curvature. We concluded that
structural distortion of GaN could induce a serious deformation, which could aect not only the
structural but also the optical and the electrical properties of the film.