Infrared Absorption and its Sources of CdZnTe at Cryogenic Temperature

TL;DR

This study investigates the infrared absorption mechanisms in CdZnTe crystals at cryogenic temperatures, revealing dominant contributions from free and trapped holes and proposing a predictive method based on room-temperature resistivity.

Contribution

The paper provides the first detailed temperature-dependent absorption coefficients of CdZnTe in specific infrared bands and introduces a model linking absorption to hole transitions, enhancing understanding of IR absorption sources.

Findings

Absorption coefficients increase at lower temperatures.

Free holes dominate absorption at 150-300 K.

Trapped holes are the main cause below 50 K.

Abstract

To reveal the infrared absorption causes in the wavelength region between electronic and lattice absorptions, we measured the temperature dependence of the absorption coefficient of $p$-type low-resistivity ($\sim 10^2~{\rm \Omega cm}$) CdZnTe crystals. We measured the absorption coefficients of CdZnTe crystals in four-wavelength bands ($\lambda=6.45$, 10.6, 11.6, 15.1$~\mu$m) over the temperature range of $T=8.6-300$ K with an originally developed system. The CdZnTe absorption coefficient was measured to be $\alpha=0.3-0.5$ ${\rm cm^{-1}}$ at $T=300$ K and $\alpha=0.4-0.9$ ${\rm cm^{-1}}$ at $T=8.6$ K in the investigated wavelength range. With an absorption model based on transitions of free holes and holes trapped at an acceptor level, we conclude that the absorption due to free holes at $T=150-300$ K and that due to trapped-holes at $T<50$ K are dominant absorption causes in CdZnTe. We also discuss a method to predict the CdZnTe absorption coefficient at cryogenic temperature based on the room-temperature resistivity.