Enhancement of electron transfer efficiency of the pseudomorphic In xGa 1− xAs/In yAl 1− yAs asymmetric step quantum well due to delta modulation doping

Abstract

The efficiencies of electrons transferring from the delta and uniform modulation-doped In y Al 1− y As layers to the In x Ga 1− x As step quantum wells in the In x Ga 1− x As/In y Al 1− y As asymmetric step quantum wells were compared. Transmission electron microscopy images and selected-area electron diffraction patterns showed that the In x Ga 1− x As active layers were grown pseudomorphologically on the In 0.52Al 0.48As buffer layer, and a possible crystal structure for the In x Ga 1− x As/In y Al 1− y As 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 In x Ga 1− x As/In y Al 1− y As 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 In x Ga 1− x As/In y Al 1− y As 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 In x Ga 1− x As/In y Al 1− y As step quantum wells in high-speed electronic devices.