Fabrication and characterization of zinc oxide-based thin film field effect transistors

Thin-film field-effect transistors have been challenged using wide band gap semiconducting oxides, such as undoped ZnO, 2% phosphorous-doped ZnO, and 2% phosphorous-doped Zn0.9Mg0.1O. High quality gate oxide is needed to enhance the performance of device. We investigated structural and electrical properties of gate dielectrics. Candidates for the gate oxide are CaHfOx and Ce0.33Tb0.67MgAl 11Ox amorphous films.; Studies of the crystallinity of CaHfOx on various substrates showed that calcium hafnate thin film has a high crystallization temperature on Si and Ge substrate. The XRD patterns of CaHfOx on biaxially textured Ni show a well-developed (101) plane at high temperatures. Results show that this perovskite oxide heteroeitaxy of the LaAlO3 substrate develops with CaHfO3(101)//LaAlO3(100). We also investigated recrystallization and dielectric behavior for amorphous CaHfOx films on Si substrates.; We studied the dielectric properties of (Ce,Tb)MgAl11O x films deposited by pulsed-laser deposition. For the ITO substrate, the leakage current density was low and the conduction mechanism was determined to be the Schottky emission model. Interface trap densities between insulator and Si were ∼1 x 1012 eV-1 cm -2 and ∼3 x 1012 eV-1 cm-2 using the Terman and conductance methods, respectively.; We also studied depletion-mode field-effect transistors with undoped ZnO and 2% phosphorous-doped ZnO for an active channel layer. The conductivity of undoped ZnO was observed as a function of channel thickness. Undoped and doped ZnO showed n-type behavior from C-V measurement. Its high carrier concentrations produced a low Ion/Ioff ratio.; We report on enhancement-mode ZnO-based field-effect transistors that utilize an acceptor-doped channel. In particular, the active channel is polycrystalline ZnO doped with Mg, to increase the band gap, and P, to decrease the electron carrier concentration. Devices are realized that display an on/off ratio of 103 and a channel mobility on the order of 5 cm 2/V s. HfO2 serves as the gate dielectric. Capacitance-voltage properties measured across the gate indicate that the ZnO channel is n type. The use of acceptor doping improves control of initial channel conductance while having a minimal impact on channel mobility relative to undoped ZnO polycrystalline channels.