Optical and electrical properties of amorphous GdxGa0.4−xO0.6 films in GdxGa0.4−xO0.6/Ga2O3 gate dielectric stacks on GaAs

Optical and electrical properties of amorphous GdxGa0.4−xO0.6 films have been systematically investigated as a function of Gd mole fraction x (0⩽x⩽0.31). The GdxGa0.4−xO0.6 films are part of GdxGa0.4−xO0.6/Ga2O3 gate dielectric stacks grown onto the GaAs(001) surface by molecular-beam deposition. When the Gd mole percent is raised from 0 to 25 at. % (0⩽x⩽0.25), the refractive index n and the optical band gap increase from 1.908 to 1.987 and from 4.22 to 5.08 eV, respectively. The electrical properties of GdxGa0.4−xO0.6 films improve dramatically with increasing Gd concentration: The leakage current falls from 7.8×10−1 to 9.7×10−10 A/cm2 (measured at an electric field of 1 MV/cm) when the Gd mole percent is raised from 8.8 to 31 at. %, and the dielectric breakdown field exceeds 4 MV/cm for x>0.21.