In the present paper, we discuss the influence of point defects on electrical and optical characteristics of ZnO thin films grown by the atomic layer deposition (ALD) method on glass and silicon substrates at low temperature (100°C). Room temperature photoluminescence (RT PL) spectra, secondary ion mass spectroscopy (SIMS), and Hall Effect measurements were made for as-grown ZnO layers. The annealing process was performed in air as well as in N2 atmosphere at 400°C for half an hour. The long annealing resulted in a larger reduction in electron concentration. Simultaneously, an evident increase in carrier's mobility was observed, which may suggest that annealing resulted in a decreased number of native defects in the ZnO layers. Also, it was observed that hydrogen atoms in ZnO samples did not dominate their electrical properties with the increase of electrons concentration.