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 $B_{\Vert }$ at low temperatures $\mathrm{}\left(T\right).$ The modulation is caused by the $B_{\Vert }$-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 $\overrightarrow{k}$ 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 $B_{\Vert },$ 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 $B_{\Vert }=0,$ 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 $B_{\Vert }$ 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 $B_{\Vert }$ 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 $B_{\Vert }$’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 $B_{\Vert }$’s because it arises from the inter-QW transitions. Reasonable agreement is obtained with recent data from ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ DQW’s.