Room temperature THz Bloch amplifiers/oscillators – ROOTS

The scientific issue of this project is to develop the potential of semiconductor superlattice as an emerging technology for room temperature tunable THz amplifiers/oscillators relying on Bloch oscillations of electrons. We will make use of advanced theory, design and processing strategies to fully exploit Bloch gain in semiconductor superlattice devices. More than 30 years after the original proposal of Bloch oscillators by Esaki and Tsu, the continuous operation of the Bloch oscillator, emitting electromagnetic radiation, tunable by an external dc electric field has still not been demonstrated. The main obstacle in the experimental realization is the formation of high-field electric domains in superlattice, associated with a negative dc differential conductivity. In this project, we propose innovative approaches exploiting the strong expertise developed within the consortium on advanced modeling, growth, fabrication and characterization of semiconductor superlattice. We will engineer original superlattice devices in which the formation of space charge instabilities is avoided, the transit time limitation is circumvented and the injection of carriers in the active regions is optimized. We will develop surface plasmon waveguide and microcavity technology to improve the coupling between the oscillating charges and the terahertz electromagnetic field. Two kinds of structure will be engineered: doped semiconductor superlattice towards the realization of room temperature tunable THz amplifiers/oscillators and undoped semiconductor towards the realization of THz sources driven by two frequency off-set continuous optical waves. We will make use of time domain terahertz spectroscopy set-up and Fourier transform infrared spectroscopy to demonstrate functional THz amplification and emission. Scattering process and their impact on Bloch oscillations will be investigated in order to determine how these oscillations can be self-sustained and aimed as a feedback for improving the design of superlattice structures, essentially in terms of material composition and band engineering. The implementation of coherent, miniature source of THz radiation that can operate at room temperature should provide more attractive modern THz systems, and thus is a great importance for applications.