Plasma wave oscillations in a nonequilibrium two-dimensional electron gas: Electric field induced plasmon instability in the terahertz frequency range

We have developed a theory of collective electron oscillations in two-dimensional semiconductor heterostructures subjected to a high electric field. The effect of the stationary electric field has been taken into account on both steady-state and high-frequency electron transport. The analysis has been conducted by solving Boltzmann-Vlasov equations in the collisionless approach for high-frequency electron transport. Two actual types of heterostructures with ungated and gated two-dimensional (2D) electron gas have been considered. We have found that the collective excitation spectra of 2D electron gas are of the multibranch character with high-quality plasmonic modes and a set of thermal modes. Applied electric field induces the following effects: strong nonreciprocal behavior of both oscillation frequency and damping; interaction of plasmonic and thermal modes; instability of excitations propagating along the electron drift (effect of negative Landau damping). The mechanism of this plasma wave instability is different from early discussed Cherenkov, Dyakonov-Shur, and Ryzhii-Satou-Shur mechanisms of instabilities in plasmonic systems. It has been shown that the electrically induced plasmon instability provides amplification of terahertz (THz) radiation in grating-based plasmonic structures. We suggest that presented results can be important for deeper understanding of THz plasma physics and developing of electrically pumping devices for THz optoelectronics.