Hydrogenic impurity binding energy in self-assembled GaAs/Ga1-xAlxAs quantum rings

Using a variational approach within the effective mass approximation and adiabatic approximation, the binding energy of the ground state of a hydrogenic impurity positioned in a self-assembled GaAs/Ga1-xAlxAs quantum ring (QR) is studied. The binding energy is calculated as a function with the size (outer radius, height) of the QR, the Al concentration, and the donor impurity position. The results indicate that the binding energy reaches a peak value when the size (outer radius, height) of the QR decreases to a certain value. The binding energy reaches a maximum for an impurity ion positioned at the midplane perpendicular to the symmetry axis of the QR. In addition, the binding energy becomes large as the Al concentration in GaAs/Ga1-xAlxAs increases. When shifting the impurity ion from the internal surface of the QR to the external surface, the impurity binding energy increases, then decreases to a certain value, indicating that there is a maximum. (C) 2008 American Institute of Physics.