Low-temperature investigations of the quantum Hall effect in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}-\mathrm{I}\mathrm{n}\mathrm{P}$ heterojunctions

We report investigations of the temperature dependence of the quantized Hall effect in modulation-doped ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{A}\mathrm{s}-\mathrm{I}\mathrm{n}\mathrm{P}$ heterojunctions. The diagonal conductivity ${\sigma }_{\mathrm{xx}}$ is studied at several maxima and minima of the magnetoresistance ${\rho }_{\mathrm{xx}}$ down to 50 mK. An interesting result is the observation of a hopping conduction mechanism when the Fermi level is in the tail of the broadened Landau levels.