Gd on GaN(0001) surface: Growth, interaction, and Fermi level movement

Growth, interfacial reaction, and Fermi level movement of Gd on n-type GaN(0001)-(1×1) surface are studied using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy-electron diffraction. Gd grows in a layer-by-layer-like mode and reacts with the substrate at the interface, leading to formation of metallic Ga at room temperature. A downward Fermi level movement is observed, and the resultant Schottky barrier height is 1.5 eV. Annealing promotes further diffusion and an interfacial Gd–Ga exchange reaction, reducing the Schottky barrier height.