EN
The detailed studies of low temperature (T=2~K) polarization resolved photoluminescence and photoluminescence excitation studies from heavily modulation doped Ga_{1-x}Al_xAs/GaAs single heterojunctions in continuous wave and time-resolved conditions are reported. The free conduction band GaAs electrons recombination with two-dimensional holes observed in low magnetic fields enabled us to determine experimentally the valence subband Landau levels. The high magnetic field photoluminescence spectra are dominated by excitonic transitions which are attributed to neutral excitons rather than to positively charged ones.