Electron-hole separation studies near the (formula presented) quantum Hall state in modulation-doped GaAs/(Al,Ga)As single heterojunctions in high magnetic fields

Magnetophotoluminescence (MPL) studies as a function of carrier concentration are reported for a series of very high mobility n-type modulation-doped GaAs/(Al,Ga)As single heterojunctions. The measurements were made in high magnetic fields to (formula presented) and at temperatures in the 0.4–2.1 K range. At low fields (formula presented) the MPL recombination is dominated a free carrierlike excitonic transition as an energy close to the free exciton in bulk GaAs. The energy and intensity of this excitation undergoes Shubnikov–de Haas-type oscillations at even integer filling factors (formula presented) with increasing field. At (formula presented) an second strong exciton transition appears at a lower energy primarily in (formula presented) polarization due to a spin (formula presented) electron recombining with a valence-band hole. It rapidly gains intensity between (formula presented) but disappears at (formula presented) At (formula presented) another redshifted transition emerges that has been described as a recombination of an electron in an initial “free hole state.” Its intensity in (formula presented) polarization increases and reaches a maximum between (formula presented) Such behavior becomes more pronounced as the carrier density increases. The redshift at (formula presented) has been correlated with recent theoretical models describing the theory of photoluminescence of two-dimensional electron systems. It has been used to determine the electron-hole separation as a function of carrier concentration.