Water Growth on GeO2/Ge(100) Stack and Its Effect on the Electronic Properties of GeO2

Abstract

Water growth on GeO2 films on a Ge(100) substrate and their effect on the electronic properties of GeO2 films are investigated using ambient-pressure X-ray photoelectron spectroscopy at relative humidity (RH) values from 0% to approximately 45%. Water adsorbs at low RHs and continues to grow gradually up to ∼1% RH, probably forming hydroxyls. Water grows rapidly above 1% RH, indicative of the formation of a molecular water film. The molecular water film formed reaches more than one monolayer in thickness at 10% RH. We show that the energy separation between Ge4+ and Ge0+ signals in Ge3d spectra increases with RH until it reaches 1%. In addition, the collapse of an initial abrupt GeO2/Ge interface is demonstrated in this humidity range, indicating that water molecules in the gas phase infiltrate into the permeable GeO2 film, and water-related species accumulate at the GeO2/Ge interface. We propose that water-related species emit electrons to the Ge bulk and positive charges are created in GeO2 close to the...