Sub-Poissonian Shot Noise in Nondegenerate Diffusive Conductors

A theory is presented for the universal reduction of shot noise by Coulomb repulsion, which was observed in computer simulations of a disordered nondegenerate electron gas by Gonz\'alez et al. [Phys. Rev. Lett. 80, 2901 (1998)]. The universality of the reduction below the uncorrelated value is explained as a feature of the high-voltage regime of space-charge-limited conduction. The reduction factor depends on the dimensionality d of the density of states, being close but not quite equal to $1/d$ in two and three dimensions.