Large-signal negative dynamic conductivity and high-harmonic oscillations in a superlattice

We discuss the properties of miniband electrons as related to the high-frequency generation in a semiconductor superlattice (SL). We study the diffusive regime in which Bloch oscillations and electrical domains do not develop and the generation may occur as a result of the negative high-harmonic nonlinear conductivity. The regime is different from the frequency conversion in stable nonlinear media and is characterized by thresholds in dc and ac driving forces. We point out the AlGaN∕GaN as a possible material system for the high-power SL terahertz source. Since the state-of-the-art III-nitride SLs have low mobility as compared to that in (AlGaIn)As SLs, the regime discussed in the paper may be the only operating condition that delivers THz-range generation in AlGaN∕GaN SLs.