Theory of impurity states in coupled quantum wells and superlattices and their infrared absorption spectra

We present a theory of impurity states in quantum wells, where the confining potential of the heterostructure and the random impurity potential are treated in a unified theory. After diagonalization of the 3D Hamiltonian we calculate the infrared absorption spectrum. We discuss the nature of impurity states that are confined in the quantum wells and their influence on the absorption spectra. We then calculate the absorption spectra for a quadruple quantum well, revealing impurity transitions as well as intersubband transitions. The results are compared to existing experimental data and show a remarkable agreement.