Noise Modelling in Low Dimensional Electronic Structures

We investigate electron transport and shot noise in single and double barrier GaAs/GaAlAs semiconductor structures. Both structures evidence shot noise enhancement and suppression. The enhanced mechanism is due solely to the positive feedback between tunneling and space charge, and it is a precursor of current instability. Concerning the suppression mechanism, the standard sequential tunneling model does not explain a suppression with a Fano factor below 0.5, which is found in several experiments. By contrast the coherent tunneling model predicts shot noise suppression below 0.5 because of Pauli principle and/or Coulomb interaction in agreement with experiments. We conclude that shot noise suppression below one-half of the full Poissonian value is a signature of coherent tunnelling against sequential tunneling in double barrier resonant diodes.