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Effects of a Diffuse Potential on Shallow-Donor States in GaAs–(Ga, Al)As Quantum Dots

The energies for the ground and excited states of a D° impurity located at the center of a GaAs/ Ga 1-x Al x As spherical quantum dot are calculated, in the effective-mass approximation, as functions of the dot radius R and spatial size. We use a variational procedure and take linear combinations of Gaussian and Slater orbitals for the impurity-envelope wave functions. A model barrier potential is proposed to study changes in the potential introduced by diffusion effects. The binding energy of a 1s 2- -like D - impurity is also studied by considering a parabolic correlation factor. It is found that the D° and D- binding energies increase as the dot size decreases up to a critical dot radius R = R c and then, for R slightly smaller than R c , the impurity wave function spreads to the barrier region and the 3D character is rapidly restored. The critical dot radius R = R c is estimated by using the uncertainty relations.