Monte Carlo Investigation of Shot-noise Suppression in Nondegenerate Ballistic and Diffusive Transport Regimes

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.