Terahertz plasma wave resonance of two-dimensional electrons in InGaP∕InGaAs∕GaAs high-electron-mobility transistors

We have observed the frequency dependence of the plasma resonant intensity in the terahertz range for a short gate-length $\mathrm{In}\mathrm{Ga}\mathrm{P}∕\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ pseudomorphic high-electron-mobility transistor. The plasma resonance excitation was performed by means of interband photoexcitation using the difference-frequency component of a photomixed laser beam. Under sufficient density of two-dimensional (2D) conduction electrons $(>{10}^{12}{\mathrm{cm}}^{-2})$ and a moderate modulation index (the ratio of the density of photoexcited electrons to the initial density of the 2D electrons) we clearly observed the plasma-resonant peaks at 1.9 and $5.8\mathrm{THz}$ corresponding to the fundamental and third-harmonic resonance at room temperature, which is in good agreement with theory.