Well-width dependence of the in-plane effective mass and quantum lifetime of electrons in GaAs/Ga1-xAlxAs multiple quantum wells

The electronic properties of modulation-doped GaAs/Ga1-xAlxAs multiple quantum wells (MWQ) with well width (L-z) in the range between 51 and 145 Angstrom have been investigated by using the Shubnikov-de Haas (SdH) oscillations technique. The carrier density and the Fermi energy have been determined from the period of the SdH oscillations. The in-plane effective mass (m*) and the quantum lifetime (tau(q)) of 2D electrons have been obtained from the temperature and magnetic field dependences of the SdH amplitude. For narrow MQW samples (L-z = 51, 75 and 78 Angstrom), m* increases with decreasing L-z; for the samples with L-z = 106 and 145 Angstrom, m* is approximately equal to that of electrons in bulk GaAs. The values obtained for tau(q) show no clear well-width dependence and suggest that interface roughness is the dominating scattering mechanism in GaAs/Ga1-xAlxAs MQWs.