Enhancement of electron and hole effective masses in back-gatedGaAs∕AlxGa1−xAsquantum wells

Both the electron and the optically created hole effective masses are found to be density dependent in a two-dimensional electron system of a GaAs/Al0.33Ga0.67As back-gated quantum well by magnetophotoluminescence spectroscopy. We show that the density-dependent electron effective mass increases with a decrease in the electron density (ns) to ns<1×1011 cm−2. It is found that the electron effective masses determined from the lowest and the second Landau levels are larger than those from the higher Landau levels. The hole effective mass is found to increase with a decrease in ns and the hole is found to localize at ns<3×1010 cm−2. We observe an upward convex curve of the photoluminescence peak energy at 2<ν<3 depending on the electron-hole distance divided by the magnetic length. These results clearly show the important roles of both electron-electron and electron-hole interactions in the recombination of a valence hole with a high-quality two-dimensional electron system