Sequential tunneling in doped superlattices: Fingerprints of impurity bands and photon-assisted tunneling

TL;DR

This study combines theory and experiments to analyze electrical transport in doped superlattices, revealing impurity band effects, negative differential conductivity, and photon-assisted tunneling phenomena.

Contribution

It provides a microscopic transport model that quantitatively explains experimental current-voltage characteristics without fitting parameters, highlighting impurity band influence and negative conductance.

Findings

Impurity bands significantly modify I-V characteristics in low-doped samples.

Negative differential conductivity occurs at high electric fields across all dopings.

Negative conductance persists over a wide frequency range of THz radiation.

Abstract

We report a combined theoretical and experimental study of electrical transport in weakly-coupled doped superlattices. Our calculations exhibit negative differential conductivity at sufficiently high electric fields for all dopings. In low-doped samples the presence of impurity bands modifies the current-voltage characteristics substantially and we find two different current peaks whose relative height is changing with the electron temperature. These findings can explain the observation of different peaks in the current-voltage characteristics with and without external THz irradiation in low-doped samples. From our microscopic transport model we obtain quantitative agreement with the experimental current-voltage characteristics without using any fitting parameters. Both our experimental data and our theory show that absolute negative conductance persists over a wide range of frequencies of the free-electron laser source.