Water-Related Hole Traps at Thermally Grown GeO₂–Ge Interface

Abstract

The generation mechanism of positive charge present in germanium oxide film thermally grown on a germanium substrate has been investigated in this study. Water-related hole traps are generated in the interfacial germanium suboxide layer. The negative flat-band voltage shift due to the charged hole traps increases with increasing electric stress field in the oxide. Both low-temperature growth of the oxide film and postmetallization annealing have been proposed for the improvement of the flat-band voltage shift. The former is effective in minimizing the suboxide layer thickness by suppressing germanium monoxide volatilization during the oxide growth. The latter method successfully reduces the density of traps caused by water desorption from the interfacial suboxide layer.

Optimal Oxide Passivation of Ge for Optoelectronics

“…1c. Assuming conditions at the interface remain constant at longer oxidation times, we confirm an increased favorability for Ge 2 O at the interface as temperature is increased to 500 • C. We are unable to detect any higher suboxides than Ge +1 up to 500 • C. Though we found a different trend for suboxides near 400 • C compared to other reports on thermal Ge oxides formed in UHV by ozone, 16 atomic oxygen, 25 and even atmospheric O 2 with an HF-last Ge surface, 31 this may indicate the significance of oxidant species, initial surface and oxidant partial pressure to interface suboxide formation.…”

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

“…Added to these, we think that hydroxyls in GeO 2 also contribute to the remaining signals, which is deduced from the permeability of GeO 2 reported in the literature. 5,22 For example, the result of temperature-programmed desorption mass spectrometry in ultrahigh vacuum showed that the amount of moisture from GeO 2 was approximately 1 order of magnitude higher than that from SiO 2 after both samples (GeO 2 and SiO 2 ) were exposed to ambient air. 5 It is easy to imagine that GeO 2 absorbs water molecules once it is exposed to water vapor and that infiltrated water molecules create hydroxyls in a GeO 2 film up to ∼1% RH.…”

“…Because the V FB shift is caused by fixed charges especially at the GeO 2 /Ge interface, its negative shift indicates that infiltrated water molecules create positive charges in the GeO 2 layer close to the GeO 2 /Ge interface. Second, Oniki et al measured the capacitance–voltage characteristics of metal/GeO 2 /Ge structures elaborately and discussed the nature of anomalous positive charges present in GeO 2 as well as its generation mechanism. , They insisted that infiltrated water molecules create neutral states in the bandgap of GeO 2 , when GeO 2 is exposed to ambient air. Those states above the Ge Fermi-level emit electrons to the Ge bulk, leading to the formation of donorlike hole-trap states located uniformly in an interfacial GeO 2 layer.…”

“…A very important finding of this study is that water-related positive charges in GeO 2 , which can cause the anomalous electrical characteristics of MOS capacitors with a GeO 2 /Ge stack, are formed at very low RHs below 1%. They are difficult to remove completely without annealing in vacuum, and can even increase in number with the application of an external bias stress, as reported in the literature. , …”

“…They are difficult to remove completely without annealing in vacuum, and can even increase in number with the application of an external bias stress, as reported in the literature. 22,28…”