Performing atomic layer deposition using a combined injector that sequentially injects source precursor and reactant precursor onto a substrate. The source precursor is injected into the injector via a first channel, injected onto the substrate and then discharged through a first exhaust portion. The reactant precursor is then injected into the injector via a second channel separate from the first channel, injected onto the substrate and then discharged through a second exhaust portion separate from the first exhaust portion. After injecting the source precursor or the reactant precursor, a purge gas may be injected into the injector and discharged to remove any source precursor or reactant precursor remaining in paths from the first or second channel to the first or second exhaust portion.