An optical alternative to the hall test

Effective mass ratios, m*, of electrons in n-type InSb, GaAs, and near intrinsic and n-type Hg_1−xCd_xTe for 0.20 < × < 0.30 over the temperature range 77K < T < 296K were measured using Faraday rotation spectroscopy. m* ranged from 0.0186 to 0.0357 for InSb with carrier concentrations, N, in the range 1.76 < N < 110 × 10¹⁶ cm⁻³ at 296K, in good agreement with available values in the literature. Effective masses of HgCdTe were found to be about twice as large at room temperature as band edge effective mass, m*_be calculations. These calculations can be corrected for thermal excitation by adding a factor, m**, to the band edge calculation: m* = m** m*_be, where m** was found empirically to be m** = 4.52 × 10₋₃T + 0.78. The electron’s mobility is proportional to the ratio of the electron’s Faraday rotation to its absorption; that is, the absorption due to the intraband transitions of the electron itself, not the sample’s total absorption, which may include holes, interband transitions, and the like. The constant of proportionality, or the “mobility constant”, was measured in n-type GaAs and InSb doped above 18 × 10¹⁶ cm⁻³ using absorption directly. Both HgCdTe and InSb have large intrinsic carrier concentrations, on the order of 10¹⁶ cm⁻³. Hole absorption is the majority component of the sample’s absorption at lower n-type dopant concentrations. In these cases, the mobility constant was determined using an absorption cross section.