Magnetotransport, excitonic transition and electronic structure studies of modulation-doped In xGa 1− xAs/In yAl 1− yAs asymmetric coupled double quantum wells

Abstract

Shubnikov–de Haas (S–dH) and photoluminescence (PL) measurements on In x Ga 1− x As/In y Al 1− y As modulation-doped coupled double quantum wells with a 100 Å In 0.65Ga 0.35As well and a 100 Å In 0.53Ga 0.47As quantum well separated by a 35 Å In 0.25Ga 0.75As embedded potential barrier were carried out to investigate both the existence of a two-dimensional electron gas (2DEG) and the excitonic transitions in the quantum wells. The S–dH oscillations and the observation of quantum Hall steps at 1.5 K demonstrated clearly the existence of a 2DEG in the In x Ga 1− x As double quantum well and the fast Fourier transformation results for the S–dH data indicated clearly that the 2DEG occupied two subbands in the In x Ga 1− x As double quantum well. Temperature-dependent PL spectra showed several excitonic transitions and a Fermi-edge singularity in the In x Ga 1− x As/In y Al 1− y As double quantum well. The electronic subband energies, the corresponding wave functions and the Fermi energy in the In x Ga 1− x As/In y Al 1− y As double quantum wells were calculated by using a self-consistent method taking into account exchange-correlation effects together with the strain and the nonparabolicity effects. The calculated electronic subband structures are in reasonable agreement with the results of the S–dH and the PL measurements. These results indicate that modulation-doped In x Ga 1− x As/In y Al 1− y As double quantum wells hold promise for potential applications such as new types of pseudomorphic high electron mobility transistors.