We review recent theoretical investigations of shot-noise suppression in
nondegenerate semiconductor structures surrounded by two contacts acting as
thermal reservoirs. Calculations make use of an ensemble Monte Carlo simulator
self-consistently coupled with a one-dimensional Poisson solver. By taking the
doping of the injecting contacts and the applied voltage as variable
parameters, the influence of elastic and inelastic scattering as well as of
tunneling between heterostructures in the active region is investigated. In
the case of a homogeneous structure at T = 300 K
the transition from ballistic to diffusive transport regimes under different
contact injecting statistics is analysed and discussed. Provided significant
space-charge effects take place inside the active region, long-range Coulomb
interaction is found to play an essential role in suppressing shot noise at
applied voltages much higher than the thermal value. In the elastic diffusive
regime, momentum space dimensionality is found to modify the suppression
factor γ, which within numerical uncertainty takes values respectively of
about ⅓, ½ and 0·7 in the 3D, 2D and 1D cases. In the
inelastic diffusive regime, shot noise is suppressed to the thermal value. In
the case of single and multiple barrier non-resonant heterostructures made by
GaAs/AlGaAs at 77 K, the mechanism of suppression is identified in the
carrier inhibition to come back to the emitter contact after having been
reflected from a barrier. This condition is realised in the presence of strong
inelastic scattering associated with emission of optical phonons. At
increasing applied voltages for a two-barrier structure, shot noise is
suppressed up to about a factor of 0·50 in close analogy with the
corresponding resonant barrier-diode. For an increasing number of barriers,
shot noise is found to be systematically suppressed to a more significant
level by following approximately a 1/(N + 1)
behaviour, N being the number of barriers. This
mechanism of suppression is expected to conveniently improve the
signal-to-noise ratio of these devices.
Research on shot noise suppression in quasi-ballistic transport nano-mOSFET
