Photoemission study of ultrathin GeO2/Ge heterostructures formed by UV-O3 oxidation

Abstract

The chemical bonding features and electronic states of ultrathin Ge oxide layers prepared on Ge(100) by UV-O3 oxidation at room temperature or thermal oxidation at 550°C and 600°C were characterized by x-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS), in comparison with those of ultrathin SiO2/Si(100) cases. We have found that the oxidation of Ge(100) by UV-O3 at room temperature proceeds in a layer by layer manner as well as the oxidation of Si(100) and that UV-O3 oxidation rates of Ge(100) and Si(100) are almost the same at room temperature in the oxide thickness region below 1 nm. From the analysis of the onset of energy loss spectra of O1s and Ge2p3/2 photoelectrons, the energy bandgap of the GeO2 films was measured to 5.70±0.05 eV in the thickness range from 0.9-1.9 nm, and the valence band offset at the interfaces between GeO2 and Ge(100) was determined to be 4.00±0.05 eV. It is also confirmed from PYS measurements that ultrathin GeO2/Ge(100) prepared by UV-O3 oxidation contains defect states being about one order of magnitude larger than ultrathin SiO2/Si(100) systems. © 2006 The Surface Science Society of Japan.