Characterization of Single-Crystalline Aluminum Thin Film on (100) GaAs Substrate

We have studied the structure and physical properties of an aluminum thin film grown on a (100) GaAs substrate. The X-ray diffraction (XRD) data shows that the Al film grown in situ by molecular beam epitaxy (MBE) is single crystalline. Compared with the polycrystalline film ex situ evaporated using an electron-gun (E-gun), the MBE-grown Al film has a high optical reflectivity in the visible and ultraviolet (UV) regime. In addition, the MBE-grown film has a 2-order-lower residue resistance, a 1-order-higher temperature coefficient of resistance, and a 2-order-larger magnetoresistance (MR) than the polycrystalline film. Owing to the long mean free time, the bulk-like electron-to-hole transition of Hall resistivity is observed for the first time in a nanoscale metal thin film. Our results suggest that MBE-grown Al thin films have great potential applications in metal-based nanoelectronics and nanophotonics.