Non-contact characterization of carrier mobility in long-wave infrared HgCdTe films with terahertz time-domain spectroscopy

We use terahertz time-domain spectroscopy to measure the complex dielectric function of long-wave infrared Hg_1-xCd_xTe films (x - 0.18, 0.20, 0.22) as a function of temperature in a non-contact manner. Using a Drude-Lorentz model fit to the measured complex transmission function combined with a Kane model description of the band structure, we obtain the temperature-dependent conduction band carrier density, effective mass, scattering time and carrier mobility for all three Hg_1-xCd_xTe films. The optical properties of a bare substrate of Cd_0.96Zn_0.04Te were also measured in the terahertz region. The high quality of the Hg_1-xCd_xTe films is demonstrated by ultrahigh mobilities exceeding 10⁵ cm²V^-1s^-1 and ionized donor densities less than 3 × 10¹⁵ cm^-3 at temperatures below 100 K.