Effects of hydrostatic pressure on donor states in symmetrical GaAs-Ga0.7Al0.3As double quantum wells

We have calculated the effects of hydrostatic pressure on the binding energies and density of impurity states for shallow donors uniformly distributed in symmetrical GaAs-(Ga,Al)As double quantum-well structures, within the effective-mass approximation and variational approach. A central finite potential barrier and two infinite external barriers define the profile of the potential barrier we have considered for the wells. In this work, we consider different well and barrier widths, shallow-donor impurity positions, and hydrostatic pressures, and study the Γ-X crossover in the (Ga,Al)As central barrier. We show that the density of impurity states presents a structure of two or three peaks associated with special positions of the impurity along the growth direction of the structure. Our results indicate that a proper knowledge of the impurity distribution inside the structure is of relevance in a quantitative comparison between theoretical and experimental results concerning the binding energies and optical-absorption spectra related to donor impurities in multiple quantum-well systems under hydrostatic pressure.