Voltage tuneable terahertz emission from a ballistic nanometer InGaAs∕InAlAs transistor

Terahertz emission from $\mathrm{InGaAs}∕\mathrm{InAlAs}$ lattice-matched high electron mobility transistors was observed. The emission appears in a threshold-like manner when the applied drain-to-source voltage $U_{\mathrm{DS}}$ is larger than a threshold value $U_{\mathrm{TH}}$ . The spectrum of the emitted signal consists of two maxima. The spectral position of the lower-frequency maximum (around 1 THz) is sensitive to $U_{\mathrm{DS}}$ and $U_{\mathrm{GS}}$ , while that of the higher frequency one (around 5 THz) is not. The lower-frequency maximum is interpreted as resulting from the Dyakonov–Shur instability of the gated two-dimensional electron fluid, while the higher frequency is supposed to result from current-driven plasma instability in the ungated part of the channel. The experimental results are confirmed by and discussed within Monte Carlo calculations of the high-frequency current noise spectra.