Carrier dynamics in coalescence overgrowth of GaN nanocolumns

• Published in: Thin solid films Vol. 519; no. 2; pp. 863 - 867
• Main Authors: Wang, Hsiang-Chen, Tang, Tsung-Yi, Yang, C.C., Malinauskas, T., Jarasiunas, K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2010; Elsevier
• Subjects: Carrier dynamics; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Coalescence; Coalescing; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Four wave mixing; Gallium nitride; Gallium nitrides; Materials science; Mechanical and acoustical properties; Metal organic chemical vapor deposition; Methods of deposition of films and coatings; film growth and epitaxy; Nanocolumns; Nanocomposites; Nanomaterials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Other semiconductors; Other topics in nanoscale materials and structures; Patterning; Photoluminescence; Physical properties of thin films, nonelectronic; Physics; Sapphire; Specific materials; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Threading dislocations; Transmission Electron Microscopy; Nanocolumns; Carrier dynamics; Metal organic chemical vapor deposition; Patterning; Threading dislocations; Photoluminescence; Gallium nitride; Transmission Electron Microscopy; Four wave mixing; Four-wave mixing; Nanocolumn; Nanostructures; Optimization; Transients; Stress relaxation; Carrier lifetime; Optical properties; Photoelectronic properties; Defect density; Epitaxial layers; Lithography; Mechanical properties; Layer thickness; MOCVD; Time resolved spectra; III-V compound; Columnar structure; Time resolution; Transmission electron microscopy; Threading dislocation; Growth mechanism; Coalescence; Microstructure; III-V semiconductors
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2010.08.149

Coalescence overgrowth of pattern-grown GaN nanocolumns on c-plane sapphire substrate with metal organic chemical vapor deposition is demonstrated. The subsequent coalescence overgrowth opens a possibility for dislocation reduction due to the lateral strain relaxation in columnar geometry. We present further growth optimization and innovative characterization of metal organic chemical vapor deposition layers, overgrown on the columnar structure with varying diameters of columns. Nano-imprint lithography was applied to open circular holes of 250, 300, 450, and 600 nm diameter on the SiO 2 layer, deposited on the GaN layer on the c-plane sapphire template. After the growth of ~ 1 μm high GaN nanocolumns, the further coalescence conditions led to an overgrown layer ~2 μm thickness. Photoelectrical and optical properties of the overgrown layers and a reference sample were investigated by time-resolved picosecond transient grating and time-integrated photoluminescence. We note a 3–4 fold increase in carrier lifetime in the overgrown epilayers when the diameter of columns increased from 250 to 450 nm. This feature is a clear indication of an ~4-fold reduced defect density.