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

Abstract

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 α is nearly proportional to the square of wavelength, increases with increasing donor concentration N_D 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 N_D and depends weakly upon λ; the electrical susceptibility has a positive sign. The direct transition still seems to contribute appreciably in Range II.