We investigate the effect of the laser parameters of pulsed laser deposition on the film stoichiometry and electronic properties of LaAlO3/SrTiO3 (001) heterostructures. The La/Al ratio in the LaAlO3 films was varied widely from 0.88 to 1.15, and was found to have a strong effect on the interface conductivity. In particular, the carrier density is modulated over more than two orders of magnitude. The film lattice expansion, caused by cation vacancies, is found to be the important functional parameter. These results can be understood to arise from the variations in the electrostatic boundary conditions, and their resolution, with stoichiometry. (C) 2013 AIP Publishing LLC.