In nanostructures, the surface-to-volume ratio is increased, and surface state problems become more serious, making success of the future Ill-V nanoelectronics strongly dependent on surface passivation. To solve this problem, we have been investigating a passivation scheme using a Si interlayer called Si interface control layer (Si ICL) [H. Hasegawa, Thin Solid Films 367 (2000) 58]. However, main efforts have been limited on (0 0 1) surfaces. This paper investigates the applicability of the Si ICL approach to (1 1 1)B surfaces. An ultrathin (1 nm) silicon layer was grown by MBE on GaAs and AlGaAs (1 1 1)B surfaces with (2 x 2), (root 19 x root 19) and (1 x 1) surface reconstructions. Surfaces were characterized by in situ X-ray photoelectron spectroscopy (XPS) technique. Si layers grew epitaxially with Si-Ga bonds at the Si/GaAs interface and Si-As termination on top, suggesting surfactant roles played by As atoms. On nitridation of Si layer by nitrogen radicals at room temperature, Si-As bonds were replaced by Si-N bonds leading to partial nitridation of the Si layer. Unlike the case of the As-stabilized GaAs (0 0 1)-(2 x 4) surface, large reduction of band bending by 250-420 meV took place on (1 1 1)B surfaces, indicating large reduction of surface states. The results indicate effectiveness of the Si ICL passivation on (1 1 1)B surface. (c) 2006 Elsevier B.V. All rights reserved.