Photoionization cross section of hydrogenic impurities in spherical quantum dots

We have used a variational wave function for hydrogenic impurities in spherical quantum dots to calculate the dependence of the photoionization cross section of such impurities on the energy and polarization of the photon. The calculation has been performed using both the infinite and finite confining potential well models. The results are presented for various dot radii and for different locations of the impurity in the dot. We find that for hydrogenic impurities at the center of a spherical quantum dot, the transitions take place between the impurity level associated with the ground subband and the free particle state in the second subband and the cross section is independent of the polarization of the photons. For off center impurities, the transitions take place between the impurity level associated with the ground subband and the free particle state in the ground subband when the photons are polarized along the direction connecting the impurity with the center of the dot while for photons polarized perpendicular to this direction, we find that the transitions take place between the impurity level associated with the ground subband and the free particle state in the second subband. Therefore the threshold energy for the photoionization cross section is lower for off center impurities when the photons are polarized along the direction connecting the impurity with the center of the dot than it is for on center impurities or for off center impurities for photons polarized perpendicular to this direction. (C) 2003 American Institute of Physics.