Confined electron and shallow donor states in graded GaAs/AlxGa1-xAs spherical quantum dots Jian-Min Shi, V. N. Freire and G. A. Farias Eur. Phys. J. B, 14 2 (2000) 337-348 Published online: 15 March 2000 DOI: 10.1007/s100510050138