Magnetic-field-induced insulator-quantum Hall conductor-insulator transitions in doped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells

We present magnetotransport measurements on ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multiple quantum wells doped with impurities at the centers of GaAs layers. Magnetic-field-induced insulator-quantum Hall conductor-insulator transitions with a well defined scaling behavior were observed. The critical exponents as well as the resistivities at the two critical magnetic fields are close to each other. Their values are, however, different from the values obtained from similar studies performed on modulation-doped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures.