Shot noise in negative-differential-conductance devices

We have compared the shot-noiseproperties at T=4.2 K of a double-barrier resonant-tunneling diodeand a superlattice tunnel diode, both of which exhibit negative differential-conductance (NDC) in their current–voltage characteristics. While the noise spectral densityof the former device was greatly enhanced over the Poissonian value of 2eI in the NDC region, that of the latter device remained 2eI. This result implies that charge accumulation, not system instability, is responsible for shot-noiseenhancement in NDC devices.