This paper reports a recent study on the polarizability and the photoionization cross section (PCS) of a hydrogenic impurity confined in a spherical AlAs/GaAs core/shell quantum dot under external electric field and hydrostatic pressure. In the framework of effective mass theory, a variational approach is used to determine the polarizability, binding energy, and the PCS of a single donor in a spherical core/shell quantum dot. Our numerical calculations reveal that all these fundamental parameters are deeply dependent on the core and shell radii. The study of the localization of the impurity inside the core/shell indicates that the Stark shift is more important when the impurity is positioned at the center of the core/shell and becomes less important when the donor moves toward the boundaries of the shell layer. In addition, a rapid decrease of the intensity of electric polarizability under hydrostatic pressure is observed. In order to understand the optical responses during the photoionization of the donor dopant, we investigated the PCS under hydrostatic pressure, electric field, ionized donor position, and core/shell sizes.

In this paper, a novel technique to study the evolution of the electronic mobility in GaAs microwave MESFET's devices versus both, frequency and bias condition is presented. The technique employs scattering parameters measurement over the frequency band of interest along with DC and Pulsed transconductance and output conductance device measurements. The examination of the presented results shows the need to include the variation of mobility with DC bias and frequency in device nonlinear models.