Nonlinear charging effect of quantum dots in a p-i-n diode

The current through a $p\ensuremath{-}i\ensuremath{-}n$ diode containing a layer of self-assembled InAs quantum dots in the intrinsic region is investigated. A series of peaks is observed in the differential conductance below the flat band regime which we attribute to electron tunneling in the quantum dot and wetting layer states, combining the carrier recombination and the carrier relaxation effects. This phenomenon is investigated numerically on the basis of a master equation model. Criteria for the observability of the charging of individual quantum dots are discussed. A key point is the presence of Coulomb screening as otherwise the long-range interdot interactions smear out the energy level spectrum.