A Study on La Incorporation in Transition-Metal (Y, Zr, and Nb) Oxides as Gate Dielectric of Pentacene Organic Thin-Film Transistor

The effects of La incorporation in three transition-metal (TM = Y, Zr, and Nb) oxides as gate dielectric of pentacene organic thin-film transistor (OTFT) have been investigated. La incorporated in Zr oxide and Nb oxide greatly decreases their trap density (as confirmed by low-frequency noise measurement) by passivating their oxygen vacancies, resulting in larger pentacene grains grown on them (as shown by atomic force microscopy) and thus higher carrier mobility for the OTFT due to less grain-boundary scattering. The carrier mobility of the ZrLaO- and NbLaO-OTFTs is about 70 times and 300 times higher than that of their counterparts based on ZrO₂ and Nb₂O₅, respectively. However, La incorporated in Y₂O₃ increases its trap density by roughening its surface, causing smaller pentacene grains grown and thus lower carrier mobility. On the other hand, all the three TM elements incorporated in La₂O₃ can result in more moisture-resistant gate dielectric with smoother surface, resulting in larger pentacene grains grown and thus higher carrier mobility for the OTFT.