Confined electron and shallow donor states in graded GaAs/AlxGa1-xAs spherical quantum dots

A theoretical study is performed on the confined electron and shallow donor states properties in graded GaAs/AlxGa1-xAs spherical quantum dots. The tw o lowest energy levels of a confined electron are obtained taking into acco unt the dependence of the electron effective mass on the spatial profile of the Al molar fraction. The ground state of a single Si shallow donor, whic h may be located at an arbitrary position in the structure, is calculated t hrough a variational approach. Depending on the dot interface width and loc alization, we find that the energy levels of the electron and donor states for the system under study can be blue or red shifted appreciably in compar ison to those calculated within the sharp interface picture. We show that i t is necessary to have accurate information concerning the interface of sem iconductor dots whose samples are used in the experiments, in order to achi eve a better understanding of their optical properties.