Noncontact 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- x} Cd _x Te films ( x = 0.18, 0.20, 0.22) as a function of temperature in a noncontact 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− x} Cd _x Te films. The optical properties of a bare substrate of Cd _0.96 Zn _0.04 Te were also measured in the terahertz region. The high quality of the Hg _{1− x} Cd _x Te films is demonstrated by ultrahigh mobilities exceeding 10 ⁵ cm ² V ⁻¹ s ⁻¹ and ionized donor densities less than 3 × 10 ¹⁵ cm ⁻³ at temperatures below 100 K.