Defect reduction in GaN/(0001)sapphire films grown by molecular beam epitaxy using nanocolumn intermediate layers

D. Cherns, L. Meshi, I. Griffiths, S. Khongphetsak, S. V. Novikov, N. Farley, R. P. Campion, C. T. Foxon

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Abstract

Transmission and scanning electron microscopies are used to examine the epitaxial lateral overgrowth of GaN on GaN nanocolumns grown on AlN/(0001)sapphire by molecular beam epitaxy. Initially, N-rich growth gave a bimodal morphology consisting of defect-free Ga-polar nanocolumns emanating from a compact, highly defective N-polar layer. Under subsequent Ga-rich conditions, the nanocolumns grew laterally to produce continuous Ga-polar overlayers. Threading dislocation (TD) densities in the overlayer were in the range of 108 - 109 cm-2, up to two orders of magnitude less than in the N-polar underlayer. It is proposed that the change in polarity is a key factor controlling the reduction in TD density.

Original languageEnglish
Article number121902
JournalApplied Physics Letters
Volume92
Issue number12
DOIs
StatePublished - 2008
Externally publishedYes

Bibliographical note

Funding Information:
The authors are grateful to the UK Engineering and Physical Sciences Research Council (EPSRC) for support for this work under Grant No. EP/D080762/1.

Funding

The authors are grateful to the UK Engineering and Physical Sciences Research Council (EPSRC) for support for this work under Grant No. EP/D080762/1.

FundersFunder number
Engineering and Physical Sciences Research CouncilEP/E000673/1, EP/D080762/1

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