Metal-insulator-semiconductor Schottky barriers are a potentially low-cost photovoltaic configuration. The PV figures of merit are strongly influenced by the interface composition and structure. Our group has used atomic layer deposition (ALD) to create well-defined alumina-based insulators in which the thickness, fixed charge, and composition can be well-controlled. Based on a simple electrostatic model, fixed charge in the insulator can be used to modify barrier heights, and the fixed charge at ALD alumina-silicon interfaces can be tuned over a range of approximately 5E12 cm-2, making this system an ideal test-bed to understand the role of fixed charge experimentally. We find little to no influence of the fixed charge characteristic of the alumina-silicon interface in our experiments, and that barrier heights appear to be dominated by interface dipoles. We relate our results to previous experimental and theoretical work that relates dipole strength to differences in oxygen areal densities at the silicon oxide-aluminum oxide interface. We also report preliminary PV figures of merit for our well-controlled MIS junctions.