Spectroscopic study of plasma wave resonances of a two-dimensional electron gas in a microcavity at low temperatures

The channel of a high electron mobility transistor can work as a resonant microcavity for plasma waves, provided that the plasmon decay length is much larger than the cavity length. We have performed a spectroscopic study in the 0.15-0.4 THz range of the power absorbed by the micrometric channel of a two-dimensional electron gas (2DEG) transistor, where the active layer is formed by a remotely doped AlGaAs/InGaAs/AlGaAs quantum well where the electron mobility increases with decreasing temperature. The radiation emitted by a tunable frequency-multiplied THz oscillator was coupled to the cavity by an integrated lens-antenna optical system. The rectified signal is measured as a function of frequency and a strong increase upon cooling to 10 K is found at specific radiation frequencies, indicating the formation of standing plasma waves in the microcavity formed by the channel.