Comparative cyclotron resonance and luminescence study of photoexcited particles in mixed type-I–type-II GaAs/AlAs multiple quantum wells

We report on the photoluminescence (PL) and photoinduced microwave absorption (PMA) of the elementary excitations in GaAs/AlAs undoped quantum wells (QW’s) in the temperature range $2<\mathrm{}{T}_L<30\mathrm{}\mathrm{K}.$ Mixed type-I–type-II QW’s are used, since separate two-dimensional electron and hole gases are formed (in the wide and narrow QW’s, respectively) by photoexcitation with densities in the range ${10}^9<n_e<~5\times {10}^{10}{\mathrm{cm}}^{\mathrm{-}2}.$ The PL spectra show transitions due to $(e1:\mathrm{hh}1)1S$ excitons $\mathrm{}\left(X\right)\mathrm{}$ and $\left[\right(e1:\mathrm{hh}1)1S+e]$ negatively charged excitons ${(X}^{-}).\mathrm{}$ The PMA dependence on magnetic field that is applied perpendicularly to the QW planes shows cyclotron resonances (CR) due to electrons and $X^{-}$ in the wide wells and heavy holes in the narrow wells. The CR traces are analyzed and yield the cyclotron effective mass, momentum relaxation rate, and relative density of the charged particles. The PL and PMA spectra are found to correlate well when observed at the same temperature and microwave power. The electron and $X^{-}$ masses and relative intensities are analyzed in terms of weak in-plane particle localization. It is found that, at low temperatures, a large fraction of the electrons and $X^{-}$ are localized by interface potential fluctuations.