Gigantic resistivity and band gap changes in GdOyHx thin films

In this letter we show that GdOyHx thin films allow one to tailor the electric and the optical properties by controlling the hydrogen and oxygen content. By changing the O/H ratio, one can shift the optical band gap from 2.4 eV in the trihydride to 5.4 eV in the pure oxide. The GdOxHy (x < 1.5, y < 2) thin films are insulating, and a resistivity as high as 10(10) Ohm cm, as compared to 10(-4) Ohm cm in the metallic state, is obtained. The thermal stability of the films depends strongly on the oxygen concentration. Samples with low oxygen content can be switched between the insulating and conducting state by reducing the hydrogen content. A reversible resistivity change of 10(6) Ohm cm is demonstrated. (C) 2000 American Institute of Physics. [S0003-6951(00)00115-7].