Free-carrier Faraday effect in n-type InSb with a pulsed 0.337 mm HCN laser

Abstract

Free-carrier Faraday rotation and ellipticity in n-type InSb samples with different electron densities have been measured in order to determine electron-impurity scattering times in the presence of magnetic fields at liquid helium temperatures. The experimental apparatus used consisted of a 4 T(40 kG) transverse-access optical cryostat in which the temperature of the sample could be held at liquid helium temperatures. Plane-polarised radiation from a pulsed far-infrared laser which produced a wavelength of 0.337 mm was passed through the sample and detected by means of a Golay cell whose output was gated, integrated and displayed on a pen recorder. Comparison of the experimental results for n-type InSb with the curves computed from the theoretical expressions yielded scattering times of the order of 10-12 s at liquid helium temperatures for two different samples. These scattering times are in good agreement with earlier measurements. There is, however, a considerable discrepancy between electron-impurity scattering times obtained by Faraday rotation and ellipticity, and field-dependent DC scattering times calculated from DC mobility measurements. Discrepancies also exist between the measured and computed values of the ellipticity squares near the cyclotron resonant field.