Microstructures of ZnO films deposited on (0001) and r-cut α-Al2O3 using metal organic chemical vapor deposition

Zinc oxide films were deposited on (0001) and r-cut α-Al2O3 under identical conditions using metal organic chemical vapor deposition. Microstructures of the ZnO films were studied in detail using conventional and high-resolution transmission electron microscopy (HRTEM), electron diffraction, and HRTEM image simulations. The films deposited on these two substrates show distinctive structural differences. The film grown on r-cut α-Al2O3 shows a high-quality single crystal with an orientation relationship of α-Al2O3[− 101–1]//ZnO[0001] and α-Al2O3(10–1–2)//ZnO(2–1–10). The interface between the film and the substrate was abrupt and decorated with high density of misfit dislocations. Film grown on α-Al2O3 (0001) shows several orientation domains. Typically, one domain correspond to the classic growth model such that α-Al2O3 (0001)//ZnO(0001) and α-Al2O3 [11–20]//ZnO[10–10]. Another domain corresponds to the growth mode such that α-Al2O3 [11–20]//ZnO[10–10] but the (0001) plane of ZnO is tilted relative to the (0001) plane of α-Al2O3 such that ZnO(0001) is almost parallel to the α-Al2O3 (− 1104) plane. This orientation reduces the extent of lattice mismatch as compared with the classic growth mode. The interface between ZnO and α-Al2O3 is abrupt and possesses periodic dislocations.