ABSTRACT
Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect, and cyclotron resonance measurements on InxGa1-xAs/In0.52Al0.48As asymmetric double quantum wells grown by metalorganic chemical vapor deposition have been carried out to investigate the electrical properties of a free electron gas and to determine the effective mass of the electron gas, subband energies and wave functions in the quantum wells. Transmission electron microscopy measurements showed that a 100- Å In0.8Ga0.2As and a 100- Å In0.53Ga0.47As quantum wells were separated by a 35- Å In0.25Ga0.75As potential barrier in an active region. The S-dH measurements at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas in the quantum wells. The results of the cyclotron resonance measurements show that the saturation of the absorption near resonance is a direct evidence of the large electron concentration in the quantum well. The electron effective masses determined from the slopes of the main peak absorption energies as a function of a magnetic field are 0.06171 and 0.05228 me for the first exited and ground subbands, respectively. Electronic subband energies and wavefunctions in the quantum wells were calculated by a self-consistent method taking into account exchange-correlation effects together with the strain and nonparabolicity effects. The 1st excited subband wavefunction in the asymmetric quantum well is strongly coupled over both In0.8Ga0.2As and In0.53Ga0.47As wells, and the results of the cyclotron resonance measurements satisfy qualitatively the nonparabolicity effect of the double quantum well.
