We report our recent investigations of a new structure formed by b-doping the barrier of an AlGaAs/GaAs heterostructure. In this new structure we have observed both a mobility of 1.9×lO6cm2/Vsec and the fractional quantum hall effect. We compare low temperature mobilities and densities achieved with the δ-doped heterostructure with corresponding high values reported in the literature for the homogeneously- doped heterostructure. We show that systematic enhancements in both density and mobility occur in the b-doped heterostructure. By δ-doping both barriers of a quantum well we have also achieved electron concentrations of 4×1012cm -2 in the well.