Resonant and non-resonant impurity states related to quantum well subbands

Abstract

The energy positions and wave function shapes of ground and excited impurity states including resonant ones are studied using expansion method. The structures under study are GaAs/AlGaAs rectangular quantum wells with four different widths. In all cases impurity binding energy (with respect to related subband) has a maximum at or near the center of the well, decreases when approaching to the barrier and seemingly has a limit of 0 if impurity moves away from the well. If impurity is displaced from the well center, then non-resonant impurity states wave functions within the well move closer to impurity center while the wave functions of the resonant states below the second subband move away from it. The effect is more pronounced for the ground and first resonant states respectively for the wider wells and reaches maximum near the halfway from center to barrier.