Monte Carlo study of shot-noise suppression in semiconductor heterostructure diodes

We report a Monte Carlo study of shot-noise suppression in single and multiple barrier nonresonant heterostructure GaAs/AlₓGa_1-xAs diodes at 77 K. We provide a microscopic investigation of the mechanisms responsible for shot-noise suppression when transport under nondegenerate conditions is controlled by tunneling across barriers. At increasing applied voltages for a single barrier structure shot-noise is suppressed up to a minimum value of 0.85 with respect to the unity value of the full shot-noise level. For a two-barrier structure shot noise is further suppressed up to about a factor of 0.50 in close analogy with the corresponding resonant barrier diode. The mechanism of suppression is identified in the carrier inhibition to come back to the emitter contact after having been reflected from the second barrier. This condition is realized in the presence of strong inelastic scattering associated with emission of optical phonons. At increasing temperature shot-noise suppression is found to become less pronounced. Peaks in the frequency dependence of the current spectral density are associated with deterministic features of the carrier motion due to reflections from the first barrier and oscillations inside the GaAs well, respectively. For an increasing number of barriers shot noise is found to be systematically suppressed to a more significant level by following approximately a $1/(N+1)$ behavior N being the number of barriers. This mechanism of suppression is expected to conveniently improve the signal-to-noise ratio of these devices.