Si-modulation-doped AlGaAs/GaAs heterostructures, which are grown on (100) and (311)A GaAs substrates, behave n- and p-type modulation-doped structures, respectively. We measure magnetophotoluminescence (MPL) spectra and discuss the difference of the carrier recombinations in these structures. Both n- and p-type structures show the MPL spectra reflecting the Landau level quantization. Though interband transitions coming from the ground subband are suppressed for ν >2 in the n-type, this rule is broken in the p-type.