  Several recent experiments have reported an anomalous temperature dependence
of the Coulomb drag effect in electron-hole bilayers. Motivated by these
puzzling data, we study theoretically a low-density electron-hole bilayer,
where electrons and holes avoid quantum degeneracy by forming excitonic
molecules. We describe the ionization-recombination crossover between the
electron-hole plasma and exciton gas and calculate both the intralayer and drag
resistivity as a function of temperature. The latter exhibits a minimum
followed by a sharp upturn at low temperatures in a qualitative agreement with
the experimental observations [see, e.g., J. A. Seamons et al., Phys. Rev.
Lett. 102, 026804 (2009)]. Importantly, the drag resistivity in the proposed
scenario is found to be rather insensitive to a mismatch in electron and hole
concentrations in sharp contrast to the scenario of electron-hole Cooper
pairing.
