Electronic subband studies in In_0.52Al_0.48As/In_xGa_1-xAs In_0.52Al_0.48As/In_xGa_1-xAs one-side-modulation-doped asymmetric coupled double quantum wells

Shubnikov-de Haas (SdH) and van der Pauw Hall effect measurements on In_0.52Al_0.48As/In_xGa_1-xAs coupled double quantum wells grown by metalorganic chemical vapor deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the subband energies and wave functions in the coupled quantum wells. Transmission electron microscopy measurements showed that In_0.8Ga_0.2As and In_0.53Ga_0.47As quantum wells were separated by an In_0.25Ga_0.75As potential barrier in an active region. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas in the quantum wells. The fast Fourier transformation results for the SdH data clearly indicate the occupation of three subbands in the In_0.52Al_0.48As/In_xGa_1-xAs coupled quantum wells. Electron subband energies and wave functions in the quantum wells were calculated by a self-consistent method taking into account exchange-correlation effects. The first and second excited subband wave functions in the asymmetric quantum well are strongly coupled over both In_0.8Ga_0.2As and In_0.53Ga_0.47As wells.