Evolution of the atomic and electronic structures during nitridation of the Si(1 1 1) surface under ammonia flux

Abstract Evolution of atomic and electronic structures during high temperature Si(1 1 1) surface nitridation under ammonia flux was studied in details by the STM/STS techniques. The adsorption and intermediate phases arising at low doses preceding the (8 × 8) structure formation were determined. Dependence of the STM images contrast on the tunneling gap voltage is interpreted within framework of the WKB tunneling current theory. It is shown that the (8 × 8) structure is formed over the silicon surface but not in the surface etching pits. Homogeneous disordered high-temperature silicon nitride phase, consisting of SixNyHz fragments transforms into an inhomogeneous one at phase transition from (1 × 1)→(7 × 7)N upon surface cooling. This silicon nitride phase is concentrated mainly in the central areas of the (7 × 7) DAS structure. A peaks shift in the STS spectra of local electronic states as a function of the ammonia dose is discovered. The nature of the peaks is associated with the electronic states of dangling bonds and/or π-bonds comprising into the SixNyHz fragments. The SixNyHz fragments are the building blocks for a graphene-like g-Si3N3 layer with the (8 × 8) structure. In frame of lattice gas model a lateral interaction of the fragments provides a phase transition to a condensed ordered phase (8 × 8).