[9] [9] Zhu J L, Xiong J J, Gu B L. Confined electron and hydrogenic donor states in a spherical quantum dot of GaAs-Ga1-x Alx As ［J］. Phys. Rev. B, 1990, 41(9): 6001-6007.

[10] [10] Porras-Montenegro N, Pérez-Merchancano S T. Hydrogenic impurities in GaAs-(Ga,Al)As quantum dots ［J］. Phys. Rev. B, 1992, 46(15): 9780-9783.

[11] [11] Porras-Montenegro N, Pérez-Merchancano S T, Latgé A. Binding energies and density of impurity states in spherical GaAs-(Ga,Al)As quantum dots ［J］. J. Appl. Phys., 1993, 74(12): 7624-7626.

[20] [20] Wu H, Bao C G. Effect of electric field on the electronic spectrum and the persistent current of a quantum ring with two electrons ［J］. Chinese Physics, 2006, 15(09): 2102-2107.

[21] [21] Wu H. Effect of electric field on the spectrum and the persisent current of a quantum ring with two electrons (II)-additional effect of a charged impurity ［J］. Chinese Physics B, 2008, 17(08): 3026-3034.

[25] [25] Movilla J L, Planelles J. Dielectric mismatch effects in two-electron zero-dimensional nanosystems ［J］. Phys. Rev. B, 2006, 74(12): 125322.

[26] [26] Xie W F. D- center quantum dots in magnetic fields ［J］. Solid State Commun., 2000, 115(8): 417-421.

[27] [27] Xie W F. Second bound state of D- center in a quantum dots ［J］. Physica B, 2002, 315: 117-122.

[28] [28] Xie W F. Two-electron energy spectrum in a parabolic quantum dot under a magnetic field ［J］. Commun. Theor. Phys., 2003, 39(4): 477-480.

[29] [29] Xie W F, Liu C. Barrier D- centers in a quantum disc ［J］. Solid State Commun., 2004, 131(1): 7-10.