Influence of Coulombic broadened DX center energy levels on free electron concentration in delta-doped AlxGa1-xAs/GaAs quantum wells

The achievable two-dimensional (2D) electron concentration in a delta-doped quantum well depends on the A] content in the doping layer and is considerably lower than the nominal doping concentration. This behavior has been so far attributed to different incorporation probabilities of Si atoms depending upon the AI content. In this work, we show instead that the energy levels of the DX center together with the Coulomb interaction account for this behavior. We present calculations of the DX center density of states which are broadened by the Coulomb interaction and show that the estimated 2D) carrier concentrations agree well with experiment.