Photoluminescence spectra of n-doped double quantum wells in a parallel magnetic field

We show that the photoluminescence (PL) line shapes from tunnel-split ground sublevels of n-doped thin double quantum wells (DQW's) are sensitively modulated by an in-plane magnetic field B-parallel to at low temperatures (T). The modulation is caused by the B-parallel to-induced distortion of the electronic structure. The latter arises from the relative shift of the energy-dispersion parabolas of the two quantum wells (QW's) in (k) over right arrow space, both in the conduction and valence bands, and formation of an anticrossing gap in the conduction band. Using a self-consistent density-functional theory, the PL spectra and the band-gap narrowing are calculated as a function of B-parallel to , T, and the homogeneous linewidths. The PL spectra from symmetric and asymmetric DQW's are found to show strikingly different behavior. In symmetric DQW's with a high density of electrons, two PL peaks are obtained at B-parallel to=0, representing the interband transitions between the pair of the upper (i.e., antisymmetric) levels and that of the lower (i.e., symmetric) levels of the ground doublets. As B-parallel to increases, the upper PL peak develops an N-type kink, namely a maximum followed by a minimum, and merges with the lower peak, which rises monotonically as a function of B-parallel to due to the diamagnetic energy. When the electron density is low, however, only a single PL peak, arising from the transitions between the lower levels, is obtained. In asymmetric DQW's, the PL spectra show mainly one dominant peak at all B-parallel to's In this case, the holes are localized in one of the QW's at low T and recombine only with the electrons in the same QW. At high electron densities, the upper PL peak shows an N-type kink like in symmetric DQW's. However, the lower peak is absent at low B-parallel to's because it arises from the inter-QW transitions. Reasonable agreement is obtained with recent data from GaAs/Al0.3Ga0.7As DQW's. [S0163-1829(99)00411-7].