Enhancement of electron transfer efficiency of the pseudomorphic InxGa1−xAs/InyAl1−yAs asymmetric step quantum well due to delta modulation doping

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.