Photoluminescence spectra from 6-doped n-type A1~Ga&~As/In&Ga"As/GaAs quantum wells have been investigated in magnetic fields H(14 T and T=1.8-18 K. The Fermi level of the quasitwo-dimensional electron gas EF was slightly below the second subband. Interband Landau-level (LL) transitions between the j, th electron LL (j, =1,2) and the first hole LL, j, -l j"were analyzed. Their intensity was found to increase anomalously when the transition energy intersected that of the magnetoexciton state involving the electron from the second subband, 0,-0q. The intensity of the 0,-0& line oscillated with magnetic field and its maxima coincided with the intersection between the 0,-0j, energy and either the j, -0& or j, -1h transitions or both of them, depending on the energy separation between EI; and the second subband. Taking into account that the j, -1& and O, -OI, transitions involve no common particle, the anomalous behavior is explained by the interaction between two magnetoexciton states, 0,-0& and j, -l j, .
We have performed a pressuretuned resonance Raman scattering study in short-period GaSb/InAs SLs in the region of El and El + dl in GaSb. Resonance profiles for polarized Raman scattering by both LO and elastic interface modes reveal two electronic transitions with two different types of Frohlich-interaction-induced scattering. The LO resonance at the El gap displays strong interference and we attribute it to intrinsic intrasubband Frohlich scattering, which is dipole allowed due to the difference in the degree of localization of the electron and hole wave functions. A new resonance enhancement peak, not present in the bulk, has been observed in between the El and El + dl gaps of GaSb. This resonance appears to be dominated by extrinsic Frohlich scattering.
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