  The electron transport through the triple-barrier resonant tunnelling diode
(TBRTD) have been studied by the self-consistent numerical method for the
Wigner-Poisson problem. The electron flow through the TBRTD can be controlled
by the gate voltage applied to one of the potential well regions. For different
gate voltage values we have determined the current-voltage characteristics,
potential energy profiles, and electron density distribution. We have found the
enhancement of the peak-to-valley ratio (up to $\sim$10), the appearance of the
linear current versus bias voltage behaviour within the negative-differential
resistance region, and the bistability of the current-voltage characteristics.
The analysis of the self-consistent potential energy profiles and electron
density distribution allowed us to provide a physical interpretation of these
properties.
