Sol-gel-derived Zn(1-x)MgxO thin films used as active channel layer of thin-film transistors

Sol-gel derived n-type Zn(1-x)MgxO (x = 0-0.45) thin films and thin-film transistors (TFTs) with active channel layers made of the films were investigated. The films were prepared at 500 degrees C. The effects of Mg doping on the crystallinity, optical transparency, grain size, and charge-carrier concentration (n) of the films were examined. The Fermi level of the films, as derived from the temperature dependence of n, was similar to 0.12eV below the conduction band. The donor concentration and donor level (E-d) were derived by a curve fitting method based on the electrical neutrality condition. Ed was found to be similar to 0.3 eV below the conduction band. The composition dependence of the TFT output characteristics was interpreted and correlated to the width of the depletion region adjacent to the grain boundaries. When the grains were almost depleted at x = 0.2, the TFT showed an enhancement mode and an on/off ratio of 10(6).