Anisotropic strain and phonon deformation potentials in GaN

Authors

V. Darakchieva, IFM, Linköping University, SE-581 83 Linköping, Sweden
T. Paskova, Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany
Mathias Schubert, University of Nebraska - LincolnFollow
H. Arwin, IFM, Linköping University, SE-581 83 Linköping, Sweden
P.P. Paskov, IFM, Linköping University, SE-581 83 Linköping, Sweden
B. Monemar, IFM, Linköping University, SE-581 83 Linköping, Sweden
D. Hommel, Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany
M. Heuken, Aixtron AG, D-52072 Aachen, Germany
J. Off, 4th Physical Institute, University of Stuttgart, 70569 Stuttgart, Germany
F. Scholz, 4th Physical Institute, University of Stuttgart, 70569 Stuttgart, Germany
B.A. Haskell, University of California, Santa Barbara, California
P.T. Fini, University of California, Santa Barbara, California
J.S. Speck, University of California, Santa Barbara, California
S. Nakamura, University of California, Santa Barbara, California

Document Type

Article

Date of this Version

May 2007

Comments

Published in PHYSICAL REVIEW B 75, 195217 2007. ©2007 The 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.