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.

By means of the microscopic transport description supplied by a semiclassical two-dimensional Monte Carlo simulator, we provide an in depth explanation of the operation (based on electrostatic effects) of the nanoscale unipolar rectifying diode, so called self-switching diode, recently proposed in A. M. Song, M. Missous, P. Omling, A. R. Peaker, L. Samuelson, and W. Seifert, Appl. Phys. Lett. 83, 1881 (2003). The simple downscaling of this device and the intrinsically high electron velocity of InGaAs channels allows one to envisaging the fabrication of structures working in the THz range. We analyze the high-frequency performance of the diodes and provide design considerations for the optimization of the downscaling process.

The potentialities of AlGaN/GaN nanodevices as THz detectors are analyzed. Nanochannels with broken symmetry (so called self switching diodes) have been fabricated for the first time in this material system using both recess-etching and ion implantation technologies. The responsivities of both types of devices have been measured and explained using Monte Carlo simulations and non linear analysis. Sensitivities up to 100 V/W are obtained at 0.3 THz with a 280 pW/Hz^1/2 noise equivalent power.