Extra-Low Temperature Growth of ZnO Thin Films by Atomic Layer Deposition

We report on ZnO thin films grown by the atomic layer deposition method at temperature of 200 degrees C and below. Low-temperature ZnO layers show bright excitonic photoluminescence for "as-grown" samples. Defect-related bands usually observed in the green and the red regions are of low intensity and are absent for ZnO layers grown at 140 degrees C - 200 degrees C, which is evidence that competing radiative decay channels are ineffective. We relate this to a blocking of the vacancy formation, which is thermally suppressed at low growth temperature. Hall measurements show that the free-carrier concentration strongly depends on the growth temperature and has the lowest value of 2 . 10(17)/cm(3) for films grown at 100 degrees C and below.