Growth of Transparent and Conductive Polycrystalline (0001)-ZnO Films on Glass Substrates Under Low-Temperature Hydrothermal Conditions

Flat panel display technology seems to be an ever-expanding field developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting film (TCF) that is today still dominated by indium-tin-oxide (ITO). In a race to find alternatives that would avoid the indium pitfalls, mainly due to its increasing price and limited natural availablity, replacement materials have been extensively investigated. This work demonstrates that by exploiting basic principles of crystal growth in geometrically constrained conditions, zinc oxide (ZnO) could easily be utilized for this purpose. ZnO layers were grown on inexpensive glass substrates via low-temperature citrate-assisted hydrothermal (HT) method. It was shown that in the nucleation stage the crystal growth can be efficiently controlled by spatially confined oriented growth (SCOG) mechanism to produce smooth and dense (0001) oriented polycrystalline ZnO films with superb optical properties. Our products show optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only in the order of few 100 Omega sq(-1). We believe that a very high degree of self-organization between the ZnO crystals in our polycrystalline films grown under controlled SCOG conditions is main reason for the highest so far reported transparency to conductivity ratio for undoped ZnO thin film ceramics.