  We report on simple experiment on temperature-dependent Hall effect
measurements in GaMnAs single crystalline samples with Mn composition estimated
at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity
band transport is visible for Mn compositions of ~0.3 at.% as a clear metallic
behaviour. The results show interesting situation that the Metal-Insulator
transition in GaAs:Mn occurs within the impurity band which is separated from
the valence bands for Mn concentrations studied here. We also discuss on the
equilibrium high temperature solubility limit of Mn in GaAs, unknown precisely
in the literature.
