Bloch gain in dc-ac-driven semiconductor superlattices in the absence of electric domains

TL;DR

This paper theoretically explores how applying a strong THz pump field to dc-biased semiconductor superlattices can achieve Bloch gain for THz radiation without electric domain formation, enabling potential THz oscillator development.

Contribution

It demonstrates that ac fields can induce positive differential conductivity and Bloch gain in superlattices, facilitating THz amplification without domain issues, which is a novel approach.

Findings

Positive differential conductivity can be achieved with strong THz pumping.

Bloch gain profile remains robust near the gain maximum.

Short THz pulses can suppress electric domains and sustain oscillator operation.

Abstract

We study theoretically the feasibility of amplification and generation of terahertz radiation in dc-ac-driven semiconductor superlattices in the absence of electric domains. We find that if in addition to dc bias a strong THz pump field is applied, Bloch gain profile for a small THz signal can be achieved under conditions of positive static differential conductivity. Here the positive differential conductivity arises, similarly to the case of large-signal amplification scheme [H. Kroemer, cond-mat/0009311)], due to modifications of dc current density caused by the application of high-frequency ac field [K. Unterrainer \textit{et al.}, Phys. Rev. Lett. \textbf{76}, 2973 (1996)]. Whereas the sign of absorption at low and zero frequencies is sensitive to the ac fields, the gain profile in the vicinity of gain maximum is robust. We suggest to use this ac-induced effect in a starter for THz Bloch oscillator. Our analysis demonstrates that the application of a short THz pulse to a superlattice allows to suppress the undesirable formation of electric domains and reach a sustained large-amplitude operation of the dc-biased Bloch scillator.