Optical measurements on the antiferromagnetic semiconductor MnTe

G. Zanmarchi

The light transmission and reflection of the antiferromagnetic semiconductor MnTe with Néel temperature TN = 307°K, have been measured for wavelengths ranging from the visible spectrum to 24 μ, and for different temperatures T from 80°K up to 375°K. The band-edge energy EG is 1·35 ± 0·10 eV at T = 80°K and 1·25 ± 0·10 eV at T = 300°K. MnTe is a p-type hexagonal semiconductor both above and below TN. The dispersion and absorption due to the free holes are analyzed in terms of the Drude theory. From reflection measurements at T = 80°K on low-resistivity samples, with the c-axis perpendicular and parallel to the electric vector of the light, the values obtained for the effective mass are m ⊥* = (0·25 ± 0·05)mO and m∥* = (1·0 ± 0·2)mO respectively. The temperature dependence of the reflectivity near TN indicates an increase of the plasma wavelength λp with increasing temperatures. Assuming the carrier concentration to be the same as at T = 80°K, a strong increase of the effective mass is obtained near TN. © 1967.

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Materials
Curve 1
Temperature K: 300 Wavelength Range, μm: 12.9-22.7 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: p-type single crystal (0.5 cm thick); doped with Cr (~10¹⁹ cm⁻³ free holes concentration at N₂ temp); electrical resistivity ~300 ohm cm at 77 K and ~20 ohm cm at N₂ temp (307 K); mobility ~2 cm² v⁻¹ sec⁻¹ at N₂ temp (307 K); polished; c-axis parallel to the specimen surface; data extracted from smooth curve; [Author's designation: Sample 3].
Curve 2
Temperature K: 80 Wavelength Range, μm: 2.90-22.3 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: p-type single crystal (0.5 cm thick); doped with Na (1.6 x 10¹⁹ cm⁻³ free holes concentration at 77 K); 6 x 10⁻² ohm cm electrical resistivity at 77 K; 2.3 x 10⁻² ohm cm electrical resistivity at N₂ temp (307 K); mobility 250 cm² v⁻¹ sec⁻¹ at 77 K and 5 cm² v⁻¹ sec⁻¹ at N₂ temp (307 K); polished, c-axis parallel to the specimen surface; data extracted from smooth curve; [Author's designation: Sample 4].
Curve 3
Temperature K: 300 Wavelength Range, μm: 4.60-22.4 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 4
Temperature K: 80 Wavelength Range, μm: 0.7-11.3 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: p-type single crystal (0.5 cm thick) doped with Na (8 x 10¹⁹ cm⁻³ free holes concentration at 77 K); electrical resistivity at N₂ temp (307 K); mobility 5 cm² v⁻¹ sec⁻¹ at N₂ temp (307 K); polished, c-axis perpendicular to the specimen surface; data extracted from smooth curve; [Author's designation: Sample 5].
Curve 5
Temperature K: 300 Wavelength Range, μm: 0.400-15.1 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 6
Temperature K: 80 Wavelength Range, μm: 3.00-24.0 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: p-type single crystal (0.5 cm thick); doped with Na (6 x 10¹⁹ cm⁻³ free holes concentration at 77 K); electrical resistivity; 8 x 10⁻² ohm cm at 77 K and 1 x 10⁻¹ ohm cm electrical resistivity at N₂ temp (307 K); mobility 150 cm² v⁻¹ sec⁻¹ at 77 K (307 K); polished, c-axis parallel to the specimen surface; measured with light polarized perpendicular to the c-axis; data taken from smooth curve.
Curve 7
Temperature K: 80 Wavelength Range, μm: 2.90-24.6 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except measured with light polarized parallel to the c-axis.