Low-resistivity ZnO films were grown by photo atomic layer deposition (photo-ALD) technique using diethylzinc (DEZ) and H2O as reactant gases. Self-limiting growth was achieved for the temperature range from 105 degrees C to 235 degrees C. It was found that UV light irradiation was very effective to increase the electron concentration of the films and the electron concentration of 5 x 10(20) cm(-3) was achieved even in undoped ZnO. Thus, the resistivity of the films grown with UV irradiation was one order of magnitude less than that grown without UV irradiation. The minimum resistivity of 6.9 x 10(-4)Ohm cm was obtained by photo-ALD method without any intentional doping.