Enhanced terahertz emission by Landau quantization in semiconductor superlattices

• We find expressions for the THz emission in biased semiconductor superlattices.
• We study the THz emission with and without magnetic field.
• THz emission in superlattices is the addition of Bloch and excitonic components.
• The magnetic field enhances the intensity and coherence of the THz light emitted.
• An ideal Bloch oscillator can be realized at high magnetic field.

We present a theoretical description of the process of therahertz emission in biased semiconductor superlattices that follows an ultra-fast interband excitation. The results show that the average current performs Bloch oscillations whose amplitude depends on the intrinsic characteristic of the superlattice as well as on the light pulse parameters. In these calculations we use a fully three-dimensional picture and include the excitonic effects. We also studied the terahertz intensity when the sample is subjected to a magnetic field parallel to its axis. We considered in detail the high magnetic field regime, where the in-plane motion is frozen in Landau orbits spectrally well separated. In this regime, a set of quasi one-dimensional Bloch oscillators can be ideally generated (oscillators with decoupled vertical and lateral electron motions), making the terahertz emission more intense and more coherent.