Anisotropic Strain and Phonon Deformation Potentials in GaN

Authors

• V. Darakchieva, Linköping University
• T. Paskova, University of Bremen
• Mathias Schubert, University of Nebraska-LincolnFollow
• H. Arwin, Linköping University
• P. P. Paskov, Linköping University
• B. Monemar, Linköping University
• D. Hommel, University of Bremen
• M. Heuken, Aixtron AG, Aachen, Germany
• J. Off, University of Stuttgart
• F. Scholz, University of Stuttgart
• B. A. Haskell, University of California, Santa Barbara
• P. T. Fini, University of California, Santa Barbara
• J. S. Speck, University of California, Santa Barbara
• S. Nakamura, University of California, Santa Barbara

Document Type

Article

Date of this Version

5-27-2007

Citation

Physical Review B (2007) 75: 195217

Comments

Copyright © 2007, American Physical Society. Used by permission

Abstract

We report optical phonon frequency studies in anisotropically strained c-plane- and a-plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E₁(TO), E₁(LO), and E₂ phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c_E1(TO) , c_E1(LO) , and c_E2 are determined. A distinct correlation between anisotropic strain and the A₁(TO) and E₁(LO) frequencies of a-plane GaN films reveals thea_A1TO, b_A1TO, a_E1LO, andb_E1LO phonon deformation potentials. The a_A1TO and b_A1TOa_A1TO and a_E1LO phonon deformation potentials agree well with recently reported theoretical estimations [J.-M. Wagner and F. Bechstedt, Phys. Rev. B 66, 115202 (2002)], while b_A1TO and b_E1LO are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented.