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Current instability and shot noise in nanometric semiconductor heterostructures

We investigate electron transport and shot noise in a single-barrier GaAs/AlGaAs heterostructure of nanometric size in the presence of ballistic and thermalized carriers. The coupling between space charge and the dependence of the transmission coefficient on energy is found to provide the positive feedback which enhances shot noise and ultimately leads to a current instability of S type. Theoretical results are in qualitative agreement with existing experiments and confirm recent Monte Carlo simulations evidencing shot-noise enhancement in GaAs/AlGaAs heterostructures.