Shallow donors in a triple graded quantum well under electric and magnetic field

The binding energy of the donor impurity in triple graded GaAs-(Ga,Al)As quantum wells is calculated by using a variational approach. The results have been obtained in the presence of a uniform magnetic and electric field applied along the growth direction as a function of the impurity position. We show that by changing the intensity of the external magnetic and electric field, a large spread in the range of the donor binding energy may be obtained. In triple graded quantum wells (TGQWs), the donor binding energy has much stronger electric field dependence than in the square quantum well structures. Our calculations have revealed the dependence of the impurity binding not only on the magnitude but also the field direction, and impurity location in the TGQWs