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

Thin Si0.8Ge0.2 layers epitaxially grown on (100) Si substrates were oxidiz ed at temperatures from 150 to 450 degrees C under vacuum ultraviolet (VUV) radiation emitted by an excimer lamp working with Xe (lambda = 172 nm). Th e structure and composition of the grown dielectric layers were investigate d by Rutherford backscattering spectrometry, nuclear reactions analysis, el lipsometry, Fourier transform infrared spectroscopy, and x-ray photoelectro n spectroscopy. These investigations have shown that, during the VUV-assist ed oxidation process, Ge atoms were initially rejected from the grown SiO2 layer even at temperatures as low as those employed here. After a certain q uantity of Ge accumulated at the interface, nanocrystalline Ge regions were directly excised from the remaining SiGe layer becoming embedded within th e advancing SiO2 layer. The layers containing these nanocrystalline Ge part icles exhibited the same visible photoluminescence spectra as those recorde d from layers already known to contain nanocrystalline Ge or GeO2 particles , porous Ge, or nanocrystalline Ge particles exhibiting a different crystal line structure. This seems to indicate that the shell region of the nanocry stalline particle, and not its crystalline core, is the source of the photo luminescence.