The efficiencies of electrons transferring from the delta and uniform modulation-doped InyAl1-yAs layers to the InxGa1-xAs step quantum wells in the InxGa1-xAs/InyAl1-yAs asymmetric step quantum wells were compared. Transmission electron microscopy images and selected-area electron diffraction patterns showed that the InxGa1-xAs active layers were grown pseudomorphologically on the In0.52Al0.48As buffer layer, and a possible crystal structure for the InxGa1-xAs/InyAl1-yAs step quantum well was described. The results of Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements at 1.5 K and the fast Fourier transformation of the S-dH data that the carrier density and the mobility of a two-dimensional electron gas occupied in the delta modulation-doped InxGa1-xAs/InyAl1-yAs step quantum wells are larger than those in the uniform modulation-doped step quantum wells. The electronic subband energies and the energy wavefunctions in the delta modulation-doped InxGa1-xAs/InyAl1-yAs step quantum well were calculated by a self-consistent method taking into account exchange-correlation effects together with the strain and nonparabolicity effects. These results can help improve understanding of the application of delta modulation-doped InxGa1-xAs/InyAl1-yAs step quantum wells in high-speed electronic devices. (C) 2003 Elsevier B.V. All rights reserved.