Mixed types I-II multiple quantum well structures consist of alternating narrow and wide GaAs wells (NW and WW), separated by AlAs barriers. The transfer of electrons from the NW to the WW results in the formation of two-dimensional electrons from the NW to the WW results in the formation of two-dimensional electron and hole gases (2DEG and 2DHG) at the WW and NW, respectively. The present study investigated the influence of the 2DEG and the 2DHG on the optical properties of the materials. The study utilized double beam photoluminescence (PL) and microwave modulated PL, offering high-resolution spectroscopy and control of the density of the gases and their kinetic energy. The results have shown that the existence of the low-density 2DEG in the WW causes the formation of trions or plasma-like recombination. In addition, electrons transfer through the barrier leading to a barrier-NW indirect recombination emission. The latter is influenced by an electrostatic potential induced by the two-dimensional gases.
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