An optical alternative to the hall test

Abstract

Effective mass ratios, m*, of electrons in n-type InSb, GaAs, and near intrinsic and n-type Hgl_xCdxTe for 0.20 < x < 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 • 1018 cm ~ 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*~ calculations. These calculations can be corrected for thermal excitation by adding a factor, m**, to the band edge calculation: m* = m** m*~, 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 • 10 ~6 cm -3 using absorption directly. Both HgCdTe and InSb have large intrinsic carrier concentrations, on the order of 101~ 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.

Measurement of electron effective mass ratios in Hg 1-x Cd x Te for 0.20 ⩽ x ⩽ 0.30 between 77K and 296K

“…The average slope is 4.31 x 10 -3 which is within 5% of the slope of the lower plot for the intrinsic samples in Eq. (5). There now appears to be two parallel plots, intrinsic and n-type, separated by a constant gap resulting in a higher correction factor for the n-type samples.…”

“…They all result in values of m* that are within a few percent of each other. Until recently, the effective mass had not been systematically measured [5]. In the case of Faraday rotation, the most popular method of measuring m* over a range of temperatures, the measurement was complicated by the narrow band gap.…”