Magnetic field induced evolution from bulk exciton to 2DEG-free hole luminescence in modulation doped heterojunctions

We studied the evolution of the PL spectra in high mobility wide GaAs/AlGaAs heterojunctions (HJ) at View the MathML source with increasing magnetic field (View the MathML source) that was applied perpendicularly to the HJ interface. For different samples the 2DEG density ranges from (0.7–View the MathML source, and it can be varied by He–Ne laser illumination due to optical depletion. At B=0, the PL is completely dominated by free exciton recombination in the undoped GaAs layer. For a filling factor ν⩽2 a strong PL transformation is observed: the exciton PL intensity decreases and a low-energy PL due to the 2DEG-free hole recombination sharply appears and quickly gains intensity at the expense of the exciton PL. We propose that this is due to a “condensation” of the bulk excitons on the magnetized 2DEG layer at ν⩽2 where the free exciton dissociates into a 2D-electron and hole.