14 April 1999 Optical anisotropy of GaN/sapphire studied by generalized ellipsometry and Raman scattering
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Abstract
Generalized variable angle spectroscopic ellipsometry (VASE) and Raman scattering have been employed to study the optical anisotropy of GaN/Sapphire structures. The GaN films were grown hydride vapor phase epitaxy and molecular beam epitaxy on both m-plane and c-plane sapphire ((alpha) -Al2O3) substrates, respectively. Anisotropic optical phonon structure of sapphire have been measured, based on which the optical axis of sapphire substrate has been determined. A 541 cm-1 TO phonon of GaN grown on m-plane sapphire substrate has been discovered experimentally which is due the coupling of A1 and E1 TOs. Optical axis orientation of GaN film on m-sapphire has been fully determined by the anisotropic angular dependence of the coupled TO phonon. Off-diagonal elements Apst and Aspt of transmission VASE (TVASE) are very sensitive parameters related to the optical anisotropy. The optical axis orientation of GaN on m-sapphire has also been accurately determined by TVASE at two special sample positions. The optical anisotropy due to GaN film and sapphire substrate has been successfully separated at 90 degree(s) samples position allowing to study the optical anisotropy of GaN film only.
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Chunhui Yan, H. Walter Yao, James M. Van Hove, Andrew M. Wowchak, Peter P. Chow, John M. Zavada, "Optical anisotropy of GaN/sapphire studied by generalized ellipsometry and Raman scattering", Proc. SPIE 3621, Light-Emitting Diodes: Research, Manufacturing, and Applications III, (14 April 1999); doi: 10.1117/12.344490; https://doi.org/10.1117/12.344490
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