Photoemission Study of Ultrathin GeO2/Ge Heterostructures Formed by UV-O-3 Oxidation

The chemical bonding features and electronic states of ultrathin Ge oxide layers prepared on Ge( 100) by UV-O-3 oxidation at room temperature or thermal oxidation at 550 degrees C and 600 degrees 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-O-3 at room temperature proceeds in a layer by layer manner as well as the oxidation of Si(100) and that UV-O-3 oxidation rates of Ge(100) and Si(100) are almost the same at room temperature in the oxide thickness region below 1nm. From the analysis of the onset of energy loss spectra of O1s and Ge2p(3/2) photoelectrons, the energy bandgap of the GeO2 films was measured to 5.70 +/- 0.05 eV in the thickness range from 0.9 similar to 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-O-3 oxidation contains defect states being about one order of magnitude larger than ultrathin SiO2/Si(100) systems.