Abstract
We have investigated the conditions necessary to achieve stronger Cherenkov-like instability of plasma waves leading to emission in the terahertz regime for semiconductor quantum wells. The surface response function is calculated for a bilayer two-dimensional electron gas (2DEG) system in the presence of a periodic spatial modulation of the equilibrium electron density. The 2DEG layers are coupled to surface plasmons arising from excitations of free carriers in the bulk region between the layers. A current is passed through one of the layers and is characterized by a drift velocity vD for the driven electric charge. By means of a surface response function formalism, the plasmon dispersion equation is obtained as a function of frequency ω, in-plane wave vector q∥=(qx,qy), and reciprocal lattice vector nG, where n=0,±1,±2,… and G=2π/d, with d denoting the period of the density modulation. The dispersion equation, which yields the resonant frequencies, is solved numerically in the complex ω-plane for the real wave vector q∥. It is ascertained that the imaginary part of ω is enhanced with decreasing d and with increasing doping density of the free carriers in the bulk medium for a fixed period of the spatial modulation.
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