  We have studied the electronic properties of the 2D electron liquid present
at the LaAlO$_3$/SrTiO$_3$ interface in series of samples prepared at different
growth temperatures. We observe that interfaces fabricated at 650{\deg}C
exhibit the highest low temperature mobility ($\approx 10000 \textrm{
cm}^2/\textrm{Vs}$) and the lowest sheet carrier density ($\approx 5\times
10^{12} \textrm{ cm}^{-2}$). These samples show metallic behavior and
Shubnikov-de Haas oscillations in their magnetoresistance. Samples grown at
higher temperatures (800-900{\deg}C) display carrier densities in the range of
$\approx 2-5 \times 10^{13} \textrm{ cm}^{-2}$ and mobilities of $\approx 1000
\textrm{ cm}^2/\textrm{Vs}$ at 4K. Reducing their carrier density by field
effect to $8\times 10^{12} \textrm{ cm}^{-2}$ lowers their mobilites to
$\approx 50 \textrm{ cm}^2/\textrm{Vs}$ bringing the conductance to the
weak-localization regime.
