TUNABLE GRID GATED DOUBLE-QUANTUM-WELL FET TERAHERTZ DETECTOR

Several aspects of the theory of plasmon resonant DC photoconduction are discussed here, in connection with recent observations involving a THz-irradiated grid-gated double-quantum-well FET.¹ In this, we construct a classical model of nonlinear polarizability to second order in the THz field using a “hydrodynamic” type formulation including the roles of a stress-tensor and friction/viscosity. The resulting second order polarizability exhibits resonant behavior when the THz frequency matches plasmon frequencies of the system, sharply reducing the effectiveness of screened impurity scattering potentials which can admit resonant DC photoconduction. Furthermore, we also show that an asymmetric double-quantum-well system with lateral periodicity can mix optical and acoustic plasmons, giving rise to an interlayer THz field which becomes very strong when tuned by gate voltage into the “mode-mode-repulsion” regime wherein the optical and acoustic modes equally share amplitude. This can enhance interlayer electron tunneling and may contribute to photoconductivity.