Dispersion Analysis of Magnesium Stannide Reflectivity

Herbert G. Lipson, Alfred Kahan

The optical reflectivity of Mg2Sn measured between 10 and 45 μ at temperatures of 80, 296, and 473°K shows the effects of both lattice-vibration and free-carrier absorption. For the range of carrier concentrations investigated, 1017 to 1019 cm-3, the plasma edge, broadened by the short relaxation time of the carriers, occurs on both sides of the transverse-optical lattice frequency, and the effects of both absorption mechanisms are superimposed. Values for the lattice dispersion parameters and carrier effective masses and relaxation times are obtained from the best fit to the experimental reflectivity curves. The relative contribution of the two mechanisms to the total reflectivity is illustrated for a heavily doped Mg2Sn sample at low temperature and in addition, the masking of the lattice vibration reflectivity as a function of free-carrier concentration and relaxation time is discussed. © 1967 The American Physical Society.

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Materials
Curve 1
Temperature, K: 80 Wavelength Range, µm: 15.1-42.0 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Doped p-type, carrier concentration ~6 x 10¹⁸ cm⁻³; [Authors' designation: Sample 291].
Curve 2
Temperature, K: 296 Wavelength Range, µm: 11.0-45.0 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Above specimen and conditions.
Curve 3
Temperature, K: 473 Wavelength Range, µm: 14.9-38.2 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Above specimen and conditions.
Curve 4
Temperature, K: 80 Wavelength Range, µm: 11.0-41.0 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Doped n-type, carrier concentration ~3 x 10¹⁸ cm⁻³; [Authors' designation: Sample B-2].
Curve 5
Temperature, K: 296 Wavelength Range, µm: 11.0-47.6 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Above specimen and conditions.
Curve 6
Temperature, K: 473 Wavelength Range, µm: 11.0-39.1 Geometry θ θ' ω: 8° 8° Composition (weight percent), Specifications and Remarks: Above specimen and conditions.