Impurity-Sensitive Infrared Absorption in n-type α-SiC

Atsuo Imai

Optical measurements were made on several crystals of n-type α-SiC in the ranges 1 to 5μ(Range I) and 15 to 30μ (Range II) at 300°K and at 500°K. The absorption coefficient a is nearly proportional to the square of wavelength, increases with increasing donor concentration ND and decreases with the rise in temperature in Range I. These results can be explained by the direct transition of electrons from donor levels to conduction band rather than the intraband transitions of the free carriers. The relative magnitudes of α in Ranges I and II support the above conclusion. In Range II, the value of α increases with the increase in ND and depends weakly upon λ the electrical susceptibility has a positive sign. The direct transition still seems to contribute appreciably in Range II. © 1966, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

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Materials
Curve 1
Temperature K: 300 Wavelength Range, µm: 15.1-30.1 Geometry θ θ' ω: ~0°~0° Composition (weight percent), Specifications, and Remarks: n-type single crystal; grown in a Lely's type furnace from commercial grade or purified SiC; carrier density at 300 K 1.4 x 10¹⁸ cm⁻³; measured in argon-nitrogen; incident beam perpendicular to the c-plane; [Author's designation: B-106].
Curve 2
Temperature K: 300 Wavelength Range, µm: 14.5-32.5 Geometry θ θ' ω: ~0°~0° Composition (weight percent), Specifications, and Remarks: Similar to above specimen and conditions except carrier density at 300 K 2.5 x 10¹⁹ cm⁻³; [Author's designation: B-97].
Curve 3
Temperature K: 300 Wavelength Range, µm: 14.0-31.1 Geometry θ θ' ω: ~0°~0° Composition (weight percent), Specifications, and Remarks: Similar to above specimen and conditions except 15 µm thick; carrier density at 300 K 1.2 x 10²⁰ cm⁻³; [Author's designation: B-87].