Electronic properties of the Sm∕4H-SiC surface alloy

Abstract

The formation of a samarium on silicon carbide (Sm∕SiC) alloy after deposition of 2–3 monolayers of Sm in ultrahigh vacuum on clean reconstructed carbon(000-1)- and silicon(0001)-terminated SiC surfaces is studied by x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, and low-energy electron diffraction (LEED). The measured work function together with core-level spectroscopy is used to differentiate the formation of samarium silicide carbide (Sm–Si–C) surface alloys on both polar faces of 4H-SiC. Both naturally n-type-doped bulk Si-face and low-doped epilayer Si-face SiC were studied. A (1×1) LEED pattern is obtained on the C-face Sm–Si–C alloy and on the Si-face epilayer Sm–Si–C alloy. Flatband voltages are estimated as a function of annealing, from the shift in the C1s and Si2p bulk core-level positions. The valency of Sm is estimated during the formation of the Sm–Si–C surface alloy. The valence of the Sm overlayer after deposition at room temperature is estimated to be approximately 2.75, while upon annealing, the Sm∕SiC surface alloys on the bulk crystal become predominately 3+ valent. In the case of the Sm∕SiC surface alloy on the Si-face epilayer, the (1×1) surface alloy is of mixed valency (2.84). In all the cases studied, the Sm 3d peak undergoes a major shift of 1.8eV accompanied with a change in the Sm 3d multiplet spectrum.