Abstract
Germanium oxide (GeO2) is one of the key materials in Ge-based transistors. However, GeO2 is permeable and soluble in water, unlike the more familiar silicon oxide (SiO2). This implies that GeO2 films will react with water vapor in air. In this review, water growth on ultrathin GeO2 films on a Ge(100) substrate as well as the effect of water layers on the electronic properties of GeO2 films are investigated by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at relative humidities (RHs) from 0% to approximately 45%. After the basic concept of AP-XPS, as well as its experimental setup, is explained, I show that water adsorbs at low RHs and continues to grow gradually up to approximately 1% RH, and probably forms hydroxyls. Water grows rapidly above 1% RH, indicative of the formation of a molecular water film. In addition, AP-XPS spectra reveal anomalous positive charging of the GeO2 film starting at a very low RH of around 10−6%, and its mechanism is discussed.
