By means of the microscopic transport description supplied by a semiclassical 2D 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 (SSD), recently proposed in [A. M. Song, M. Missous, P. Omling, A. R. Peaker, L. Samuelson, and W. Seifert, Appl. Phys. Lett. 83, 1881 (2003)]. This device provides a rectifying behavior without the use of any doping junction or barrier structure (like in p-n or Schottky barrier diodes) and can be fabricated with a simple single-step lithographic process. The simple downscaling of this device and the use of materials providing high electron velocity (like high In content InGaAs channels) allows to envisage the fabrication of structures working in the THz range. With a slight modification of the geometry of the SSD, a lateral gate contact can be added, so that a nanometer self-switching transistor (SST) can be easily fabricated. We analyze the high frequency performance of the diodes and transistors and provide design considerations for the optimization of the downscaling process.