X-ray diffraction studies of epitaxial laterally overgrown (ELOG) GaN layers on sapphire substrates

• Published in: Journal of crystal growth Vol. 245; no. 1; pp. 37 - 49
• Main Authors: Domagala, J.Z, Zytkiewicz, Z.R, Beaumont, B, Kozlowski, J, Czernetzki, R, Prystawko, P, Leszczynski, M
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2002; Elsevier
• Subjects: A1. Dislocations; A1. High resolution X-ray diffraction; A1. Stresses; A1. X-ray transmission; A3. Epitaxial lateral overgrowth; A3. Metalorganic vapor phase epitaxy; B1. Gallium compounds; B1. Nitrides; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Vapor phase epitaxy; growth from vapor phase; A3. Epitaxial lateral overgrowth; A1. Dislocations; 68.55.−a; A1. X-ray transmission; 61.72.−y; B1. Nitrides; A1. Stresses; A3. Metalorganic vapor phase epitaxy; 81.15.Gh; B1. Gallium compounds; A1. High resolution X-ray diffraction; 61.10.−i; Inorganic compounds; Epitaxial lateral overgrowth method; Crystal orientation; Gallium nitrides; Crystal chemistry; VPE; Crystal growth from vapors; XRD; Experimental study; Lattice parameters; Lateral growth; Crystal perfection; High-resolution methods; Thin films; Dislocation density; MOVPE method; Heterojunctions; Overlayers; Microstructure; III-V semiconductors
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/S0022-0248(02)01705-0

GaN layers grown by metalorganic vapor phase epitaxy on sapphire substrates in epitaxial lateral overgrowth (ELOG) mode were studied using the high-resolution X-ray diffraction technique in double and triple axis modes (including reciprocal lattice mapping), both in reflection and transmission geometries. GaN layer grown on unmasked sapphire was examined in the same way for a comparison. We have found that in the fully overgrown ELOG structures: (i) hexagonal unit cells are deformed, so the lattice parameters a ⊥ (perpendicular to the stripes) and a 30 (inclined by 30° to the stripes) are smaller by up to 0.1% and 0.02%, respectively, as compared to those in the GaN buffer, (ii) curvature radii of the samples are of 1.2–1.4 m in the direction parallel to the stripes and of 1 m in the direction perpendicular to the stripes, which is consistent with the strain observed, and (iii) sapphire miscut along the 〈11.0〉 direction (i.e. perpendicular to the stripes) causes an additional inclination of ELOG lattice planes with respect to those in the buffer. A qualitative explanation of these findings is presented taking into account increase of GaN grain size in the ELOG layers.