Terahertz plasmon modes in grating coupled double quantum well field effect transistors

This dissertation explores plasmon modes resonantly excited by terahertz radiation in double quantum well field effect transistors. The plasmon modes are probed as a function of gate voltage, temperature, frequency, in-plane magnetic field and polarization of the terahertz radiation.;The samples used were GaAs/Al 0.3Ga0.7As double quantum wells patterned into (2 x 2) mm mesas with a metal grating gate and ohmic contacts to both wells.;We observe sharply resonant, voltage tuned terahertz photoconductivity that we can semi-quantitatively model by two dimensional standing plasma oscillations under the grating gate. The resonant frequency is directly related to the electron densities and the period of the grating. The resonant photoconductivity requires a double quantum well but the mechanism whereby plasma oscillations produce changes in device conductance is not understood.;The resonant response peaks at ∼30 K. An in-plane magnetic field produces a dramatic inversion and shift of the photoconductive plasma resonance. The effect of the polarization of the terahertz radiation is puzzling; a single resonant peak with the polarization perpendicular to the grating lines, a double peak with parallel polarization. These effects remain unexplained at this time.;While aspects of this tunable and sharply resonant terahertz photoconductivity are not well understood, the results presented in this dissertation suggest that one could develop a fast, tunable terahertz detector based on two dimensional plasma oscillations of coupled double quantum wells.