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Spectroscopy of Charged Donors and Many-Electron Effects in Semiconductor Quantum Wells

100%

McCombe B., Jiang Z., Tischler J., Weinstein B., Hawrylak P.

Acta Physica Polonica A

1999

vol. 96

issue 5

559-572

Far infrared magnetospectroscopic studies of negative donor ions (D^{-}), and donors in the presence of many excess electrons in high magnetic fields in GaAs/AlGaAs quantum wells are reviewed. Both singlet and triplet transitions of well-center D^{-}ions were observed and are in good agreement with recent theoretical calculations. For off-well-center D^{-}ions evidence for a predicted magnetic-field-induced "unbinding" of the second electron was found. In the presence of many excess electrons the D^{-}singlet and -triplet transitions are blue-shifted substantially and evolve into bound magnetoplasmon excitations. Cusps are observed at integral and fractional Landau-level filling factors (ν) in a plot of normalized blue-shift of the D^{-}singlet-like bound magnetoplasmon transition vs. ν. For ν<1, the singlet-like bound magnetoplasmon transition continuously approaches the isolated D^{-}singlet transition with increasing magnetic field, while the triplet-like transition loses strength, irrespective of the electron density. Exact diagonalization studies of a donor ion with a few electrons in a parabolic lateral confining potential show the importance of electron-electron interactions and localization due to the long-range fluctuating potential in explaining this behavior. High pressure studies in a specially designed diamond anvil cell exhibit a continuous evolution from bound magnetoplasmon transitions to isolated D^{-}transitions to neutral donor transitions in a single sample as the pressure is increased and the electron density in the wells is decreased.

Internal Transitions of Charged Excitons in AlGaAs/GaAs Lateral Fluctuation Quantum Dots

73%

Meining C., Whiteside V., McCombe B., Nickel H., Petrou A., Tischler J., Bracker A., Gammon D., Dzyubenko A.

Acta Physica Polonica A

2004

vol. 106

issue 3

383-393

Low temperature measurements of magneto-photoluminescence and optically detected resonance spectroscopy in magnetic fields up to 10~T were carried out on GaAs/Al_{0.3}Ga_{0.7}As quantum well samples grown by molecular beam epitaxy with lateral fluctuation quantum dots produced by growth interruption. Monolayer fluctuations of the quantum well width form lateral quantum dots for which confinement energies are less than Coulomb correlation energies. Five different width quantum wells (2.8-14.1 nm) were grown in a single sample, doped in the barriers with Si donors to allow for photoluminescence of both excitons and trions. We report studies of the optically detected resonance spectra associated with the ensemble photoluminescence of all of the wells including observation of bound-to-continuum internal transitions of trions, both singlet and triplet, and electron cyclotron resonance for the wider wells, which also show a clear bound-to-bound triplet transition. The latter is forbidden by magnetic translational invariance, but can be seen in these samples because this symmetry is broken by the lateral fluctuations, whose characteristic dimensions are greater than the trion orbit size. The two narrowest wells show strong broad optically detected resonance signals associated with inhomogeneously broadened internal transitions of the strongly correlated trions in the lateral dots. The optically detected resonance signals peak well below the calculated positions of electron cyclotron resonance. As expected for localized carriers and excitons, there is no free electron cyclotron resonance. We also present preliminary measurements of optically detected resonance spectra from a single dot.

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2 Acta Physica Polonica A

1 2004

1 1999

2 McCombe B.

2 Tischler J.

1 Bracker A.

1 Dzyubenko A.

1 Gammon D.

1 Hawrylak P.

1 Jiang Z.

1 Meining C.

1 Nickel H.

1 Petrou A.

1 Weinstein B.

1 Whiteside V.

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Spectroscopy of Charged Donors and Many-Electron Effects in Semiconductor Quantum Wells

Internal Transitions of Charged Excitons in AlGaAs/GaAs Lateral Fluctuation Quantum Dots