Shot noise suppression and coherent tunneling in a triple barrier resonant diode

We investigate shot noise suppression associated with coherent tunneling in a triple barrier resonant diode (TBRD). Here, due to the interaction between the two resonant states, the transmission probability, D (ϵ), can be non Lorentzian even in the case when the resonant level is far from the bottom of the emitter conduction band. We find that the resonant feature is narrower than that of the double barrier resonant diode (DBRD) [1] and it is asymmetric, i.e. non Lorentzian. The Fano factor is of about 0.3 at 4.2 K and slightly below 0.5 at 77 K. However, with respect to the DBRD both the current peak and the minimum value of the Fano factor shows up at a higher value of the applied voltage and their profiles are significantly smoothed out. The reason for that is a smoother dependence of the resonant level energy on applied voltage. For a better physical insight, we discuss the shot noise in an ideal TBRD, where the electron transparency can be unity or zero, thus shot noise is expected to be strongly suppressed. This conclusion is confirmed by the results of calculations which show that minima values of Fano factor in such structures can be significantly less than 0.5. Also, we found that an increase of electron concentration in the emitter further reduces the noise. The reason for this reduction is a decrease in thermal fluctuations of the occupation of electron states that provide the peak current where noise is minimal.