Magnetic-field-induced delocalization in center-doped G a A s / A l x Ga 1 − x As multiple quantum wells

We report magnetotransport measurements and scaling analysis on a series of center-doped GaAs quantum wells. Sharp phase transitions were observed in the magnetic field sweep and it was found that, depending on the doping concentration in the quantum wells, the insulating phase can make transitions to quantum Hall phase with Landau-level filling factors (\ensuremath{\nu}) of 2, 6, and 8. The critical exponents vary from sample to sample and are mobility dependent. The longitudinal resistivities of these samples at the phase transition points decrease with increasing \ensuremath{\nu}, and for a sample with higher mobility, its value is close to $h/\ensuremath{\nu}{e}^{2}.$