We have investigated a graded-gap superlattice with differential photocurrent spectroscopy at 77 K. The lowest conduction subband exhibits with increasing electric field a transition from localized to extended miniband states and back to localized …

We have observed an electric-field-induced change in the dimensionality of excitons in superlattices, from three to quasi-two dimensions. The exciton binding energy of a (40 Å/(40 Å) GaAs/(GaAl)As superlattice, determined from low-temperature …

Using optical techniques, we have demonstrated that the quantum coherence of electron states in GaAs/GaAlAs superlattices under electric fields increases drastically as the period, $D$, and the electric field, $\cal{E}$, decrease, reaching at least …

We have observed electric-field-induced interactions between the extended states of a (40 Å)-(15 Å) GaAs-Ga0.65Al0.35As superlattice and the localized state of an 80-Å terminating GaAs well. At fields such that the energy of an extended state was …

Using photocurrent spectroscopy, we have demonstrated that the quantum coherence in GaAs-Ga$_{1-x}$Al$_x$As superlattices increases with decreasing superlattice period $D$, and that it is maintained for at least eight periods when $D = 60$ angstroms. …

By applying a variable electric field to a 30-35 Å GaAs/Ga$_{0.65}$Al$_{0.35}$As superlattice we have achieved tunable doubly resonant Raman processes, in which both the incident and the scattered light are in resonance with electronic transitions. …

We have observed that a strong electric field E shifts to higher energies the photoluminescence and photocurrent peaks of a GaAs-Ga0.65Al0.35As superlattice of period D (=65 Å), which we explain by a field-induced localization of carriers to isolated …

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