Features of interband absorption in narrow-gap semiconductors

TL;DR

This paper analyzes the interband absorption features in narrow-gap semiconductors, revealing how dielectric properties behave near the absorption threshold, including singularities and their dependence on carrier degeneracy and temperature.

Contribution

It provides explicit evaluation of the dielectric function's dispersion in the infrared region for narrow-gap semiconductors and semimetals, highlighting singularities and their physical implications.

Findings

Imaginary part of dielectric function shows a plateau above the absorption threshold.

Real part exhibits a logarithmic singularity at the threshold.

Degenerate carriers cause divergence in the dielectric function at the threshold.

Abstract

For semiconductors and semimetals possessing a narrow gap between bands with different parity, the dispersion of the dielectric function is explicitly evaluated in the infrared region. The imaginary part of the dielectric function has a plateau above the absorption threshold for the interband electron transitions. The real part of the dielectric function has a logarithmic singularity at the threshold. This results in the large contribution into the dielectric constant for pure semiconductors at low frequencies. For samples with degenerate carriers, the real part of the dielectric function is divergent at the absorption threshold. This divergence is smeared with the temperature or the collision rate.