Microscopic analysis of shot-noise suppression in nondegenerate ballistic transport

We present a numerical simulation of shot-noise suppression due to long-range Coulomb interaction in nondegenerate ballistic transport. Calculations make use of an ensemble Monte Carlo simulator self-consistently coupled with a one-dimensional Poisson solver, and are applied to a ballistic semiconductor structure formed of a lightly doped active region surrounded by two contacts acting as reservoirs. The doping of the injecting contacts and the applied voltage are taken as variable parameters. At increasing voltages the transition from thermal to shot-noise conditions is analysed. Space-charge is found to be responsible for an important suppression of shot noise even in the presence of linear current-voltage characteristics. At increasing injection rates we have found a strong tendency towards shot-noise suppression which scales with a dimensionless Debye length. The statistical properties of the electron flow along the structure are modified by Coulomb interaction, evidencing a sub-Poissonian behaviour. The frequency dependence of the fluctuations is also analysed. The spectral density of current fluctuations exhibits structures related to the different characteristic times involved in the carrier transport.