Infrared reflectance of optical phonon modes in AlGaN epitaxial layers grown on sapphire substrates

Jun Rong Chen, Tien Chang Lu, Gen Sheng Huang, Tsung-Shine Ko, Hao Chung Kuo, Shing Chung Wang

Research output: Chapter in Book/Report/Conference proceedingConference contribution

4 Citations (Scopus)


We reported the systematical study of optical properties of hexagonal Al x Ga 1-x N 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 Al x Ga 1-x N 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 Al x Ga 1-x N 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.

Original languageEnglish
Title of host publicationGallium Nitride Materials and Devices III
Publication statusPublished - 2008 Apr 21
EventSociety of Photo-Optical Instrumentation Engineers (SPIE) - San Jose, CA, United States
Duration: 2008 Jan 212008 Jan 24

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherSociety of Photo-Optical Instrumentation Engineers (SPIE)
CountryUnited States
CitySan Jose, CA

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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