Excited states of hydrogenic impurities in quantum wells in magnetic fields

Quasi-two-dimensional hydrogenic impurity levels in quantum wells under the influence of magnetic fields are investigated. Experimentally, 1s to np (n=2, 3, 4) transition energies in quantum wells of various widths are measured by the photoconductivity technique for magnetic fields up to 9 T. Theoretically, these energies are calculated by a new variational method that is valid for the whole range of magnetic field strengths, from the zero-field limit to the high-field limit. Good agreement is achieved for every transition for well widths up to approximately 300 AA, for which the confinement effect is appreciable. Consistent discrepancies found for 450 AA are expected to be accounted for by including subband mixing because of the wide width and small subband separation. Our study demonstrates that the simple variational method can produce good results for highly excited levels in magnetic fields provided that the confinement due to the quantum well is sufficiently strong.