Growth and structure of ZnO thin films on polar (√3 × √3)R30° reconstructed and unreconstructed MgO(111) surfaces by atomic layer deposition

Polar heterointerfaces of MgO(111) and the II–VI semiconductor ZnO are of technological interest for transparent conducting electrode applications. Growth and structure of thin films on polar surfaces can be different than on nonpolar surfaces due to the large surface energy of polar surfaces. The authors have grown ZnO on unreconstructed MgO(111)-(1 × 1)-OH terminated and reconstructed MgO(111)-(√3 × √3)R30° polar oxide surfaces using atomic layer deposition (ALD). A homemade ultrahigh vacuum-interfaced viscous-flow ALD reactor with in situ quartz crystal monitor was used to grow ZnO thin films on the MgO(111) substrates. In the ALD process temperature window, the growth rate was found to be ∼2.3 A/cycle. Atomic force microscopy revealed that the surface roughness increases with ZnO film thickness and that reconstructed MgO(111) is a better substrate for production of smooth ZnO films. X-ray diffraction analysis revealed that ZnO thin films grown at 130 °C are polycrystalline, having the wurtzite structu...