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.