Magnetotransport, magneto-optical and electronic subband studies in highly strained one-side-modulation-doped double quantum wells

Abstract

Shubnikov - de Haas (SdH), Van der Pauw Hall effect and cyclotron resonance measurements on asymmetric double quantum wells grown by metalorganic chemical vapour deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the effective mass of the electron gas, subband energies and wavefunctions in the quantum well. Transmission electron microscopy measurements show that a 50 Å InAs and a 100 Å quantum well were separated by a 30 Å potential barrier in an active region. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas (2DEG) in the quantum wells. The fast Fourier transformation results for the SdH data indicate clearly the electron occupation of two subbands in the double quantum wells. The results of the cyclotron resonance measurements show that one absorption resonance is evidence of electron concentration occupied at the ground state subband in the double quantum well. The electron effective mass determined from the slope of the main peak absorption energies as a function of a magnetic field is . Electronic subband energies and energy wavefunctions in the quantum wells were calculated by a self-consistent method taking into account exchange correlation effects together with strain and non-parabolicity effects. The ground state subband wavefunction is strongly localized in the InAs quantum well side, and the first excited subband wavefunction in the asymmetric quantum well is very weakly coupled over both InAs and wells.