It was noted that the 2-dimensional electron concentration which was possible in a -doped quantum well depended upon the Al content in the doping layer, and was considerably lower than the nominal dopant concentration. This behavior had previously been attributed to the differing incorporation probabilities of Si atoms; depending upon the Al content. Here, it was shown that the energy levels of the DX center, together with a Coulomb interaction, accounted for this behavior. Calculations were made of the DX center density of states, as broadened by the Coulomb interaction, and it was found that the estimated 2-dimensional carrier concentrations agreed well with experiment.

G.Brunthaler, M.Seto, G.Stöger, K.Köhler: Applied Physics Letters, 1994, 65[24], 3084-6