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Proceedings Paper

Infrared reflectance of optical phonon modes in AlGaN epitaxial layers grown on sapphire substrates
Author(s): Jun-Rong Chen; Tien-Chang Lu; Gen-Sheng Huang; Tsung-Shine Ko; Hao-Chung Kuo; Shing-Chung Wang
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Paper Abstract

We reported the systematical study of optical properties of hexagonal AlxGa1-xN epitaxial films grown on c-sapphire substrate using metal-organic chemical vapor deposition. By performing Fourier transform infrared spectroscopy measurements, the high-frequency dielectric constants and phonon frequencies can be obtained by theoretically fitting the experimental infrared reflectance spectra using a four-phase layered model. The high-frequency dielectric constant of AlxGa1-xN varies between 4.98 and 4.52 for ε∞⊥(polarization perpendicular to the optical axis) and between 4.95 and 4.50 for ε∞,//(polarization parallel to the optical axis) respectively when the aluminum composition changes from 0.15 to 0.24. Furthermore, from experimental infrared reflectance spectra of AlxGa1-xN films, a specific absorption dip at 785 cm-1 was observed when the aluminum composition is larger than 0.24. The dip intensity increases and the dip frequency shifts from 785 to 812 cm-1 as aluminum composition increases from 0.24 to 0.58. According to the reciprocal space map of x-ray diffraction measurements, the emergence of this dip could be resulted from the effects of strain relaxation in AlGaN epitaxial layers due to the large lattice mismatch between GaN and AlGaN epitaxial film.

Paper Details

Date Published: 15 February 2008
PDF: 9 pages
Proc. SPIE 6894, Gallium Nitride Materials and Devices III, 68941U (15 February 2008); doi: 10.1117/12.760296
Show Author Affiliations
Jun-Rong Chen, National Chiao Tung Univ. (Taiwan)
Tien-Chang Lu, National Chiao Tung Univ. (Taiwan)
Gen-Sheng Huang, National Chiao Tung Univ. (Taiwan)
Tsung-Shine Ko, National Chiao Tung Univ. (Taiwan)
Hao-Chung Kuo, National Chiao Tung Univ. (Taiwan)
Shing-Chung Wang, National Chiao Tung Univ. (Taiwan)

Published in SPIE Proceedings Vol. 6894:
Gallium Nitride Materials and Devices III
Hadis Morkoç; Cole W. Litton; Jen-Inn Chyi; Yasushi Nanishi; Euijoon Yoon, Editor(s)

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