Thermal oxidation of amorphous germanium thin films on SiO<inf>2</inf> substrates

L. De los Santos Valladares, A. Bustamante Dominguez, A. Ionescu, A. Brown, A. Sepe, U. Steiner, O. Avalos Quispe, S. Holmes, Y. Majima, R. Langford, C. H.W. Barnes

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© 2016 IOP Publishing Ltd. In this work we report the thermal oxidation of amorphous germanium (a-Ge) thin films (140 nm thickness) in air. Following fabrication by conventional thermal evaporation on SiO2 substrates, the samples were annealed in air at different temperatures ranging from 300 to 1000 °C. By means of x-ray diffraction, x-ray reflectivity, synchrotron grazing-incidence wide-angle x-ray scattering and cross-sectional transmission electron microscopy analysis it is found that the a-Ge films abruptly crystallize at 475 °C, while simultaneously increasing the thickness of the oxide (GeO2) in a layer by layer fashion. X-ray photoemission spectroscopy reveals that the oxidation state of the Ge atoms in the GeO2 layer is 4+. However, a reaction at the GeO2/Ge interface occurs between 500 and 550 °C reducing the oxide layer to GeOx (x<2) and containing Ge2+ and Ge+. The thickness of the oxide layer grows with the annealing temperature following an Arrhenius behavior with an activation energy of 0.820.09 eV up to 500 °C. Remarkably, we observed simultaneous enhancement of the oxidation and crystallization of the a-Ge in the temperature interval 450 °C-500 °C, in which the oxidation rate reaches a maximum of around 0.8 nm °C-1 at around 500 °C.
Original languageAmerican English
JournalSemiconductor Science and Technology
StatePublished - 11 Nov 2016


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