Identification of subsurface damage in freestanding HVPE GaN substrates and its influence on epitaxial growth of GaN epilayers

• Published in: Journal of crystal growth Vol. 307; no. 2; pp. 309 - 314
• Main Authors: Grandusky, J.R., Jindal, V., Tripathi, N., Shahedipour-Sandvik, F., Lu, H., Kaminsky, E.B., Melkote, R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.09.2007; Elsevier
• Subjects: A3. Metalorganic chemical vapor deposition; B1. Nitrides; B2. Semiconducting III–V materials; B3. Light emitting diodes; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Photoluminescence; Physics; Theory and models of film growth; Vapor phase epitaxy; growth from vapor phase; B3. Light emitting diodes; B1. Nitrides; B2. Semiconducting III–V materials; A3. Metalorganic chemical vapor deposition; 71.55.−i; 81.65.Ps; 81.05.Ea; Atomic force microscopy; A3. Metalorganic chemical vapor deposition; Bl. Nitrides; B2. Semiconducting III-V materials; B3. Light emitting diodes; Nucleation; Gallium nitrides; Luminescence; Photoluminescence; Roughness; Polishing; VPE; Cathodoluminescence; Surface states; Thin films; Surface effect; Nitrides; 81.05.Ea; 81.65.Ps; 71.55.-i; Optical properties; Damage; Epitaxial layers; Quantum wells; Light emitting diodes; Optoelectronic devices; MOCVD; Time resolved spectra; Lifetime; Growth mechanism; Free-standing film; Nanostructured materials; III-V semiconductors
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2007.06.033

Freestanding hydride vapor phase epitaxy grown GaN substrates subjected to various polishing methods were characterized for their surface and subsurface conditions. Although different polishing processes led to very smooth surfaces as seen in atomic force microscopy and optical microscopy, they resulted in drastically different optical properties measured by photoluminescence (PL) and cathodoluminescence (CL). PL measurements showed a large increase in defect luminescence. There was also subsurface damage evidenced in CL imaging for one polishing process. Morphological and optical characteristics of an overgrown GaN thin film indicate great differences in the initial nucleation on the substrates subjected to different polishing processes even though the starting surface roughness was similar. This difference continued for the growth of a 405 nm light emitting diode (LED) structure. A PL lifetime reduction by factors of two and four, respectively, was seen for the band edge peak of the GaN layer and the quantum well peak of the LED structure as measured by time-resolved PL. This variability in device performance emphasizes the need for a greater understanding of the effects of starting surfaces, and subsurface characteristics, on the epitaxial growth.