Indium doping-induced change in the photoconduction spectra of o-TaS3

TL;DR

This study investigates how indium impurities alter the photoconduction spectra and electronic properties of the charge density wave compound orthorhombic TaS3, revealing impurity-induced states within the Peierls gap.

Contribution

It provides experimental evidence of impurity effects on the density of states inside the Peierls gap in TaS3, using diffusion methods to introduce indium and analyze spectral changes.

Findings

Increased photoconduction amplitude with indium diffusion time.

Impurity states below the optical gap consistent with T"{u}tt"{o}-Zawadowski theory.

Diffusion reduces the Peierls transition temperature.

Abstract

Impurities and defects are known to affect the properties of the charge density wave (CDW) state but the influence of impurities on the density of states inside the Peierls gap remains largely unexplored. Here we present an experimental study of the effect of indium impurities on photoconduction spectra of CDW compound orthorhombic TaS$_3$. We use the temperature diffusion method to introduce indium into a sample from preliminary attached In contacts. The concentration of In after 23 hours of diffusion is found to be nonuniform and strongly dependent on the distance to the contacts. The diffusion affects the spectral range 0.15-0.25 eV, increasing the photoconduction amplitude linearly with diffusion time. The optical gap value obtained from the measurements is $2\Delta = 0.25$ eV and the tail of states below $2\Delta$ is associated with the impurities in agreement with the T\"{u}tt\"{o}-Zawadowski theory. Diffusion-induced modification of current-voltage characteristics and decrease of the Peierls temperature are also observed. Neither changes in photoconduction spectra nor in the Peierls transition temperature of the control sample with Au contacts are found.