Nanostructured GaN nucleation layer for light-emitting diodes.
This paper addresses the formation of nanostructured gallium nitride nucleation (NL) or initial layer (IL), which is necessary to obtain a smooth surface morphology and reduce defects in h-GaN layers for light-emitting diodes and lasers. From detailed X-ray and HR-TEM studies, researchers determined that this layer consists of nanostructured grains with average grain size of 25 nm, which are separated by small-angle grain boundaries (with misorientation approximately 1 degrees), known as subgrain boundaries. Thus NL is considered to be single-crystal layer with mosaicity of about 1 degrees. These nc grains are mostly faulted cubic GaN (c-GaN) and a small fraction of unfaulted c-GaN. This unfaulted Zinc-blende c-GaN, which is considered a nonequilibrium phase, often appears as embedded or occluded within the faulted c-GaN. The NL layer contained in-plane tensile strain, presumably arising from defects due to island coalescence during Volmer-Weber growth. The 10L X-ray scans showed c-GaN fraction to be over 63% and the rest h-GaN. The NL layer grows epitaxially with the (0001) sapphire substrate by domain matching epitaxy, and this epitaxial relationship is remarkably maintained when c-GaN converts into h-GaN during high-temperature growth.
Narayan
J
J
Department of Materials Science and Engineering, EB-1, Centennial Campus, North Carolina State University, Raleigh, North Carolina 27695-7907, USA.
Pant
P
P
Wei
W
W
Narayan
R J
RJ
Budai
J D
JD
D000537:Aluminum Oxide; D003460:Crystallization; D005708:Gallium / Q000737:chemistry*; D006358:Hot Temperature; D008027:Light; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D008968:Molecular Conformation; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000295:instrumentation / Q000379:methods*; D010777:Photochemistry / Q000379:methods*; D012666:Semiconductors; D014965:X-Rays
C473348:gallium nitride; D005708:Gallium; D000537:Aluminum Oxide