Abstract
The formation process of ZnO thin films grown by pulsed-liquid injection metal–organic chemical vapour deposition (PLI-MOCVD) has a major impact on its morphological, structural, electrical and piezoelectric properties, but their correlation has not been elucidated yet nor decoupled from the thickness effects.
Highlights
Zn-polarity, while the opposite [0001%] direction defines the Opolarity.[6]
This shows that the variation of the DEZn solution and O2 gas flow rates along with their ratio in the PLI-metal–organic chemical vapour deposition (MOCVD) system drastically affects the morphology of zinc oxide (ZnO) thin films, which could be due to their influence on the microstructure of crystalline planes as well as on their free energies during the growth process.[25,31,32]
The growth texture and tuneable crystal polarity of ZnO thin films are explained by the evolutionary selection model given by van der Drift that is further revisited to take into account the variation of oxygen chemical potential through the variation of the O2/DEZn flow rate ratio.[38]
Summary
Zn-polarity, while the opposite [0001%] direction defines the Opolarity.[6]. This non-centrosymmetric structure along with the partially ionic bond of Zn2+ and O2À ions lead to the creation of spontaneous and piezoelectric polarization fields along the caxis.[5,6,7,8] For piezoelectric applications, the high uniformity of the crystal orientation along the c-axis and of the crystal polarity is a critical issue. Our previous study showed that ZnO nanowire arrays grown on silicon by MOCVD at 700 1C exhibit a higher piezoelectric amplitude as compared to its thin film counterpart grown at 500 1C, and have the Zn-polarity uniformity offering a high potential for piezoelectric applications.[29] The thin films grown at 500 1C with coexistent Zn- and O-polarity domains gradually get the predominance of Zn-polarity domains after being annealed under oxygen atmosphere at 700–1000 1C, indicating that these domains are more stable than the O-polarity domains at higher temperature.[30] Besides the growth and annealing temperatures, the flow rates of reactants is expected to strongly affect the growth direction of ZnO thin films and likely its crystal polarity. The structural properties of ZnO thin films are investigated by X-ray diffraction (XRD) and Raman spectroscopy, while their electrical resistivity is measured by transmission line measurement (TLM), showing a strong correlation with the morphology and polarity transition
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
