Lattice Vibration Spectra of Aluminum Nitride

A. T. Collins, E. C. Lightowlers, P. J. Dean

The reflectivity and transmission spectra of aluminum nitride have been measured using unpolarized radiation in the wavelength region 2 to 30 μ. The dielectric parameters and the zone-center (k≃0) opticalmode energies [transverse (TO) and longitudinal (LO)] have been calculated from the reflectivity measurements using dispersion theory. The values obtained are TO=82.7 meV (666.7 cm-1), LO=113.6 meV (916.3 cm-1), ε∞=4.84, and ε0=9.14. From these data the value calculated for the Szigeti effective charge is q*=1.2. Polarization measurements have revealed a sharp minimum in the reststrahlen band for E parallel to the c axis at ∼111.0 meV. Otherwise the reflectivity curves appear identical for both polarizations. Thirteen absorption bands have been observed on the high-energy side of the reflectivity band. A tentative interpretation is proposed in which these bands are considered to be due to combinations of six representative phonon branches at or near the Brillouin-zone boundary (k≃kmax). The phonon energies resulting from this interpretation are LO=91.4, TO1=82.5, TO2=78.1, LA=62.9, TA1=55.3, and TA2=50.9 meV. © 1967 The American Physical Society.

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Materials
Curve 1
Temperature K: 298 Wavelength Range, µm: 8.00-14.3 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Flat platelet (0.25 mm thick); crystals grown at the Allen Clark Research Center of the Plessey Company; polished; data extracted from smooth curve; [Authors' designation: Series E].
Curve 2
Temperature K: 298 Wavelength Range, µm: 2.00-29.8 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Flat plate (~0.5 mm thick); crystals grown by the Pechiney Company, France; c-axis approximately parallel to the front surface; ground and polished; data extracted from smooth curve; [Authors' designation: Series F, AN965F2].
Curve 3
Temperature K: 298 Wavelength Range, µm: 10.0-12.0 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except incident radiation polarized perpendicular to the c-axis.
Curve 4
Temperature K: 298 Wavelength Range, µm: 10.0-12.0 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except incident radiation polarized parallel to the c-axis.
Curve 5
Temperature K: 298 Wavelength Range, µm: 8.00-14.3 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Flat platelet (0.25 mm thick); crystals grown at the Allen Clark Research Center of the Plessey Company; polished; data extracted from smooth curve; [Authors' designation: Series F].
Curve 6
Temperature K: 298 Wavelength Range, µm: 2.00-29.8 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Flat plate (>0.5 mm thick); crystals grown by the Pechiney Company, France; c-axis approximately parallel to the front surface; ground and polished; data extracted from smooth curve; [Authors' designation: Series F, Advaice].
Curve 7
Temperature K: 298 Wavelength Range, µm: 10.0-12.0 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except incident radiation polarized perpendicular to the c-axis.
Curve 8
Temperature K: 298 Wavelength Range, µm: 10.0-12.0 Geometry θ': ~0°~0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except incident radiation polarized parallel to the c-axis.