Plasmons localized at point charges in semiconductor quantum wells

The plasmon excitations of inhomogeneous carrier gases in semiconductor quantum wells in the presence of charged impurities are investigated. The random phase approximation for the carrier gas yields an integral equation which expresses the condition that plasmons may be self-consistently localized in the vicinity of the impurity. The localized plasmon is a density wave trapped at the impurity site and exists in the electron (hole) gas only for negative (positive) impurity charge. Bound states of the intersubband plasmon are found for all densities of the carrier gas in a quantum well, a result which differs qualitatively from the bulk case. Numerical results for the binding energies are given for a range of parameters.