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Layer Thickness Dependence of Strain in GaN grown by HVPE

Published online by Cambridge University Press:  21 March 2011

Gyu Gwang Sim ,
P. W. Yu ,
D. C. Reynolds ,
D. C. Look ,
Sang Soo Kim  and
D.Y. Noh
Gyu Gwang Sim
Affiliation:
Department of Information and Communications, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
P. W. Yu
Affiliation:
Department of Information and Communications, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
D. C. Reynolds
Affiliation:
Semiconductor Research Center, Wright State University, Dayton, Ohio 45435
D. C. Look
Affiliation:
Semiconductor Research Center, Wright State University, Dayton, Ohio 45435
Sang Soo Kim
Affiliation:
Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
D.Y. Noh
Affiliation:
Department of Materials Science and Engineering, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
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Abstract

Wurzite GaN epilayers on sapphire substrates usually suffer from biaxial compressive strain due to the mismatches of the thermal expansion coefficients and the lattice constants between GaN layers and sapphire substrates. We have investigated the layer thickness effects on strain and transition energies by photoluminescence (PL), photoreflectance (PR) and X-ray diffraction (XRD). Samples used in this study are grown by hydride vapor phase epitaxy (HVPE) and have the layer thickness of 0.76, 2.6, 5.3 and 48 m. The PL and PR spectra showed the redshift of the transition energies with increasing layer thickness. This is attributed to strain-induced energy shift. The layer thickness dependence of strains is directly observed by XRD. The strain along the c -axis (εzz) decreased with increasing layer thickness. This indicates the strain is relaxed with layer thickness. From strain variation with layer thickness, we suggest that strain relaxation process is rapid at the initial stage of growth and becomes slower as the layer grows. The full width at half maximum (FWHM) of PL spectra and theta rocking curves decrease with increasing layer thickness. This indicates the crystal quality improves as the strain is reduced. Since the strain effect is very small at the layer thickness of 48 μm, we expect zero strain for thicker layers that can potentially be used as substrates for homoepitaxy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 693 , 2001 , I3.33.1
Copyright
Copyright © Materials Research Society 2002

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