Semi-Epitaxial SmB6 Thin Films Prepared by the Molecular Beam Epitaxy

We grow thin films of SmB6 by molecular beam epitaxy under ultra-high vacuum better than 1×10−6 Pa. Sm and B were evaporated independently by Knudsen cells with the deposition rate ratio of B and Sm as B/Sm in between 4.0 and 5.7 on an MgO (100) substrate with the substrate temperature of 1000 ∘C. Reflection high energy electron diffraction patterns show spotted ones indicating a relatively flat film surfaces. This is in good agreement with the surface roughness measured by the atomic force microscope. Interplane and inplane X-ray diffraction measurements represent the preference growth of c-axis oriented SmB4 thin films with the ratio B/Sm = 4.0. We obtained SmB6 thin films with the ratio B/Sm in between 4.9 and 5.7. X-ray diffraction measurements clarify that our SmB6 thin films show evidence of partial epitaxial growth as major domains orienting along [100]SmB6 ∥ [100]MgO. Crystallinity of inplane alignment is improved with approaching the stoichiometric deposition rate of B/Sm = 6. The electrical resistivity increases with decreasing temperature as a semiconductor, and becomes constant at low temperatures. These features well reproduce the tendency observed for the resistivity of bulk samples.