Adsorption and co-adsorption of boron and oxygen on ordered α-SiC surfaces

Influence of the 7×7-1×1 phase transition on the sticking of oxygen on Si(111)

: Ultraviolet photoemission and electron-energy-loss measurements of Si(111) - 7x7 between T = 15 and 300 K reveal significant temperature-dependent changes in the occupied surface states and their transitions which can be associated with electron-phonon coupling at the surface. Several new surface states and transitions are determined at low temperatures, including a highly localized (about 2-meV-wide), half-occupied state that resides within a 100-meV-wide surface-state band gap and determines the Fermi-level position.

Temperature-dependent surface states and transitions of Si(111)-7x7

Whilst Chap.4 deals with controlled passivation of surfaces in the solid phase, Chap.5 summarises the more extreme processing conditions that have been applied to the formation of oxides and nitrides. Two main regimes are described here. The first, laser annealing, involves oxygen or nitrogen implantation into the semiconductor, followed by laser induced melting and epitaxial regrowth of the disordered layer. An alternative method employs similar high intensity laser radiation to melt a thin layer of amorphous (or crystalline) material in the presence of e.g. oxygen. These novel non-equilibrium processing techniques have enabled film growth rates of more than mm/s to be achieved. This chapter also describes how surface cleaning can be performed by applying a succession of high intensity laser pulses to the material held in high vacuum.

Passivation by Laser Annealing and Melting

The laser annealed Si(111) 1×1 surface with chemisorbed oxygen at submonolayer coverages and its irradiation with a ruby laser has been studied with ultraviolet photoelectron spectroscopy and high-resolution electron-energy-loss spectroscopy. The surface oxide which forms directly upon O2 exposure is found to be similar to that which forms on the Si(111) cleaved 2×1 and the 7×7 reconstructed surfaces. Ruby-laser irradiation converts this surface oxide at submonolayer coverages into clumps of silicon dioxide and regions of clean silicon. Both surface oxides show electronic transitions in the visible and ultraviolet energy region which may be related to known network and point defects in vitreous and crystalline silicon dioxide.

A. J. Schell-Sorokin

Papers

Laser irradiation of chemisorbed oxygen on Si(111): electronic states and clump formation of SiO2