We have investigated the electronic properties of the δ-modulation-doped Al0.30Ga0.70As/In0.15Ga0.85As heterojunction for a variety of different configurations. Experimental findings are compared with theoretical predictions based on the two-band effective mass approximation including strain, many-body, finite temperature, and DX center effects. We have also examined the case where the δ doping is placed in an embedded GaAs well within the Al0.30Ga0.70As. This is intended to reduce the effects of DX centers. In this instance, as the doping concentration is increased, experimentally determined channel density, ns, suggests higher saturation values, which may leave a residual electron density in the GaAs well. This residual charge density is parallel with the electron density in the InGaAs well and represents an additional conducting path. The features of the theoretical channel density versus doping density curves are confirmed by 300 and 1.6 K resistivity and Hall measurements, and Shubnikov–de Haas measurements made at 1.6 K.