${\mathit{D}}^{\mathrm{-}}$ centers in spherical quantum dots

A negatively charged donor center ${\mathit{D}}^{\mathrm{-}}$ (i.e., a neutral shallow donor ${\mathit{D}}^0$ that binds a second electron) in a spherical quantum dot is studied by use of a variational approach. A trial function which includes electron-correlation effects and approaches the Chandrasekhar-type function in the limit of zero barrier height is used. The well-radius and barrier-height dependence of the ‘‘binding energy’’ of the ${\mathit{D}}^{\mathrm{-}}$ center is obtained. The dimensional characteristics are clearly demonstrated not only for the ‘‘binding energy’’ and its maximum of the ${\mathit{D}}^{\mathrm{-}}$ center but also for the ratio of ${\mathit{D}}^{\mathrm{-}}$ to ${\mathit{D}}^0$ ‘‘binding energy’’ and the electron-correlation effect.