Keywords: atomic layer deposition, photoluminescence, zinc oxide, c–oriented, X–ray diffraction, ZnO thin films, lattice–mismatched substrates, nanotechnology
Growth of (002)–oriented ZnO thin films on largely lattice–mismatched substrates using atomic layer deposition
ZnO thin films have been successfully deposited by Atomic Layer Deposition (ALD) using Diethylzinc (DEZn) and water (H2O) as precursors. The preferred orientations of the thin films were found to be strongly dependent on the deposition temperature. (100)–oriented ZnO thin films were grown in the temperature range of 155 to 220°C, whereas (002)–oriented ZnO thin films were formed between 220 to 300°C. It is worth mentioning that ALD technique allowed ZnO thin films with preferred orientation, i.e. (002), to be deposited on both Si and glass substrates which have a large lattice mismatch to ZnO. This process capability could be attributed to the unique characteristics of a slow growth rate due to the self–limiting growth and a relatively high deposition temperature (220–300°C) which provided sufficient energy for Zn and O atoms to migrate towards <0001> in the ALD process. Besides, the (002)–oriented ZnO thin films have the best crystal quality and lowest resistivity. The thickness of as–deposited films could be controlled at nanoscale as the growth rate was proportional to the ALD process cycles.