Epitaxial ZnO thin film transistors on 4H-SiC substrates

Abstract

Epitaxial ZnO thin film transistors (TFTs) were successfully fabricated on 4H-SiC (0001) substrates and characterized. When compared with conventional ZnO TFTs on glass substrates that were prepared in the same fabrication process, the ZnO TFTs on 4H-SiC substrates exhibited improved characteristics, namely, a saturation mobility of 5.41cm2/Vs, a threshold voltage of 2.43V, and a subthreshold swing of 0.61V/decade. The ZnO TFTs on glass substrates showed 0.44cm2/Vs, −1.55V, and 1.13V/decade. Such improved performance is attributed to the different growth behavior and structural properties of the ZnO channel layers on 4H-SiC substrates. Structural analysis on the ZnO channel layers clearly revealed the epitaxial growth of high-crystalline ZnO along the c-axis on 4H-SiC and the polycrystalline growth on glass substrates. The epitaxial ZnO thin films showed a higher Hall mobility of 24.17cm2/Vs due to less grain boundary and a lower carrier concentration of 6.21×1015/cm3 resulting from higher crystalline quality with less defects, whereas the ZnO on glass exhibited 6.24cm2/Vs and 2.37×1017/cm3.