Surface characterization of oxide growth on porous germanium films oxidized in air

A time iterative surface analytical study of as-deposited and chlorinated nanoporous germanium (PGe) films oxidized in Class 1000 cleanroom air at room temperature is reported. Deconvolution of X-ray photoelectron spectroscopy (XPS) Ge 3d core level spectra for as-deposited films showed stable levels of Ge2O, GeO, and Ge2O3 with air exposure duration, while growth of GeO2 was observed with logarithmic rate dependence, characteristic of low temperature oxide growth on fully dense Ge films. In contrast, chlorinated PGe showed an initially reduced surface and growth of all GeOx phases for up to 10 h of air exposure, after which only GeO2 was observed to grow with similar kinetics to that observed on the as-deposited films. Deconvolution of the XPS Cl 2p core level spectra showed continual loss of chlorine for up to similar to 10 h of air exposure after which no Cl-Ge components could be resolved. The results reported herein reveal logarithmic growth of each of the GeOx phases on chlorinated PGe during displacement of chlorine with oxygen. Once chlorine is removed from the surface, the percentages of Ge2O, GeO, and Ge2O3 suboxides remain constant with only GeO2 growth with further air exposure. These results offer insight into the early stages of oxide growth on porous germanium indicating the formation of a suboxide transition layer onto which GeO2 grows. (C) 2012 Elsevier B.V. All rights reserved.