Bloch Oscillations in Semiconductor Superlattices

A brief summary of the time-resolved investigation of Bloch oscillations of electron wave packets in semiconductor superlattices is given. Focussing on the emission of coherent terahertz-frequency electromagnetic radiation by Bloch oscillations, new experimental and theoretical results are presented. In all experiments published so far, Bloch oscillations have been induced by simultaneous impulsive optical excitation of several excitonic Wannier-Stark states at the bandedge of the first electron miniband. Here, we report on the first observation of Bloch oscillations induced by photo-excitation of continuum states as high as 100 meV above the fundamental bandgap. We then address the feasibility of optically pumped Bloch (or Esaki-Tsu) oscillators as a practical source for electromagnetic signals with a frequency continuously tunable from several hundred GHz to at least 6 THz. Advantage is taken of the supperradiant character of the emission process. The emission efficiency is discussed and concepts for an increase of the output power are proposed.