Characteristics of dielectric layers formed by low-temperature vacuum ultraviolet-assisted oxidation of SiGe layers

Abstract

Thin Si_0.8Ge_0.2 layers epitaxially grown on (100) Si substrates were oxidized at temperatures from 150 to 450 °C under vacuum ultraviolet (VUV) radiation emitted by an excimer lamp working with Xe (λ = 172 nm). The structure and composition of the grown dielectric layers were investigated by Rutherford backscattering spectrometry, nuclear reactions analysis, ellipsometry, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. These investigations have shown that, during the VUV-assisted oxidation process, Ge atoms were initially rejected from the grown SiO₂ layer even at temperatures as low as those employed here. After a certain quantity of Ge accumulated at the interface, nanocrystalline Ge regions were directly excised from the remaining SiGe layer becoming embedded within the advancing SiO₂ layer. The layers containing these nanocrystalline Ge particles exhibited the same visible photoluminescence spectra as those recorded from layers already known to contain nanocrystalline Ge or GeO₂ particles, porous Ge, or nanocrystalline Ge particles exhibiting a different crystalline structure. This seems to indicate that the shell region of the nanocrystalline particle, and not its crystalline core, is the source of the photoluminescence.