  A low-temperature upturn of the Coulomb drag resistivity measured in an
undoped electron-hole bilayer (uEHBL) device, possibly manifesting from exciton
formation or condensation, was recently observed. The effects of density
imbalance on this upturn are examined. Measurements of drag as a function of
temperature in a uEHBL with a 20 nm wide Al$_{.90}$Ga$_{.10}$As barrier layer
at various density imbalances are presented. The results show drag increasing
as the density of either two dimensional system was reduced, both within and
above the upturn temperature regime. A comparison of the data with numerical
calculations of drag in the presence of electron-hole pairing fluctuations,
which qualitatively reproduce the drag upturn behavior, is also presented. The
calculations, however, predict a peak in drag at matched densities, which is
not reflected by the measurements.
