Magneto-optical effects in semiconductors

Abstract

An experimental investigation of magneto-optical effects including free-carrier Faraday rotation, ellipticity and cyclotron resonance in n-type indium antimonide samples with different electron densities has been undertaken in order to measure electron-impurity scattering times in the presence of magnetic fields at cryogenic temperatures.

The experimental apparatus used consisted of a 4 tesla (40 kilogauss) transverse-access optical cryostat in which the temperature of the sample could be held near either liquid nitrogen or liquid helium temperatures. Plane-polarized 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.

The results have been analysed with the aid of the classical theory based on the Drude free-electron model and Maxwell's equations for conducting media, taking into account multiple internal reflections in the specimens. The results of calculations for other materials (mercury telluride and gallium arsenide) are also presented. Comparison of the experimental results for n-type indium antimonide with the curves computed from the theoretical expressions yielded scattering times of the order of 10-12sec at liquid helium temperatures for several different samples. These scattering times are in good agreement with eatlier measurements of scattering times at these temperatures obtained by other workers from measurements of cycxouronresonance linewidths and Faraday rotation. There is, however, a considerable discrepancy between electron impurity scattering times obtained by magneto-optical methods and field-dependent d.c. scattering times calculated from d.c. mobility measurements. Discrepancies also exist between the measured and com-puted values of the ellipticity near cyclotron resonance. Some explanations of the differences between theory and experiment are considered, and further possible lines of investigation are discussed.