Size-effects in photoemission and optical second harmonic generation spectroscopy of Ge nano-dots on Si(111)

Abstract

Ge nano-dots have been grown on Si(111) covered by a thin oxide layer using a wedge shaped deposition profile, resulting in varying nano-dot size along the sample profile. Samples were investigated by optical second harmonic generation (SHG) and photoemission spectroscopy (PES). The growth of the nano-dots was characterized by core level PES and scanning electron microscopy, and size effects were found in valence band PES. SHG spectra reveal two clearly resolvable resonances related to the E1 transitions in Si and Ge, respectively. Deposition of Ge leads to a field at the surface that modifies the SHG response from the Si substrate. The Ge SHG signal grows up during deposition and shifts towards lower energy with increasing particle size, demonstrating that size effects are also present in the optical transitions.