Tunable THz plasmon resonances in a InGaAs/InP heterostructure

Gate-bias tuned plasmon resonances excited by THz radiation in a two dimensional electron gas are reported. A commercial InGaAs/InP HEMT wafer is patterned with source, drain, and 500 nm period grating gate contacts.~ The grating couples THz radiation to the plasmons, defines their wavevector, and tunes the sheet charge density with applied bias.~ Fourier spectroscopy over the range 10 -- 200 cm$^{-1}$ at 4 K reveals absorption at the fundamental plasmon frequency along with several higher harmonics. These resonances shift to lower frequency with sheet-charge depletion as expected from theory and the device electrical properties.~ The device has potential as a tunable narrow-band detector for spectrometer on a chip and space situational awareness applications.