Negative high-frequency differential conductivity in semiconductor superlattices

TL;DR

This paper investigates how anharmonic Bloch oscillations in semiconductor superlattices can cause negative high-frequency differential conductivity, enabling potential high-frequency amplification even with positive static conductivity.

Contribution

It introduces a new understanding of negative high-frequency differential conductivity arising from anharmonic oscillations and proposes an optimal miniband dispersion law for high-frequency amplification.

Findings

Negative differential conductivity occurs at multiples of Bloch frequency.

Anharmonicity leads to negative high-frequency response even with positive static conductivity.

Optimal miniband dispersion law can enhance high-frequency field amplification.

Abstract

We examine the high-frequency differential conductivity response properties of semiconductor superlattices having various miniband dispersion laws. Our analysis shows that the anharmonicity of Bloch oscillations (beyond tight-binding approximation) leads to the occurrence of negative high-frequency differential conductivity at frequency multiples of the Bloch frequency. This effect can arise even in regions of positive static differential conductivity. The influence of strong electron scattering by optic phonons is analyzed. We propose an optimal superlattice miniband dispersion law to achieve high-frequency field amplification.