Direct Evidence of GeO Volatilization from GeO₂/Ge and Impact of Its Suppression on GeO₂/Ge Metal–Insulator–Semiconductor Characteristics

Abstract

From the studies on the thermal desorption behaviors of GeO 2 film and its impact on the electrical properties of GeO 2 /Ge metal-insulator-semiconductor (MIS) capacitors, it was clarified that the GeO volatilization is driven by the interface reaction at GeO 2 /Ge, and that volatilization is the origin of the interface deterioration of the MIS capacitors. We found that a Si cap layer formed on top of the GeO 2 film suppresses the GeO desorption very efficiently. Then, a marked improvement of the capacitance-voltage (C-V) characteristics was successfully demonstrated with the GeO 2 /Ge MIS capacitors fabricated by capped annealing process, where a Ni silicide electrode was used as the cap layer. These results provided us quite an important guide for realizing high-quality Ge/dielectric interfaces.

Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

“…Because of these advantages, various attempts have recently been made to fabricate Ge-based MOS devices. Although Ge oxide (GeO 2 ) is the most fundamental insulator in these devices, it decomposes at low temperatures 3,4 and is soluble in water, 5 unlike the more familiar Si oxide (SiO 2 ). In spite of these physical instabilities of the bulk, the GeO 2 / Ge interface is still attractive because of its excellent electrical properties.…”

Effects of surface oxide formation on germanium nanowire band-edge photoluminescence

“…Several studies have described the oxidation conditions for formation of the various Ge suboxide states. 23,24 These results suggest that when Ge NWs are exposed to air, the native oxide of Ge will form the Ge 2 O 3 (Ge 3þ ) stoichiometry predominantly. This oxide state will leave the germanium surface with some dangling bonds that can trap carriers and promote their non-radiative recombination.…”

“…20 A defective GeO x (suboxide)/Ge interface has "fast" interface states (ps-ns response time) that will tend to quench radiative recombination of photogenerated carrers. [21][22][23] In contrast, a GeO 2 /Ge interface provides a lower interface state density than a Ge suboxide/Ge interface. [21][22][23] Obtaining higher oxidation states (e.g., Ge 4þ ) in the oxide layer requires breaking additional Ge-Ge bonds, the rate of which can be accelerated by thermal annealing.…”

“…[21][22][23] In contrast, a GeO 2 /Ge interface provides a lower interface state density than a Ge suboxide/Ge interface. [21][22][23] Obtaining higher oxidation states (e.g., Ge 4þ ) in the oxide layer requires breaking additional Ge-Ge bonds, the rate of which can be accelerated by thermal annealing. 20,24,25 Here, we have used annealing in O 2 at moderate temperatures to control the state of oxidation of the Ge NW surface and to correlate the surface oxide stoichiometry with defect passivation using PL.…”

“…31 Due to the existence of these trap levels, the majority of photoexcited electrons in the L-valley of Ge NWs undergo non-radiative recombination and no PL signal can be detected from them. Formation of GeO 2 bonding in the surface oxide may passivate [21][22][23] these defects, removing trap levels from the bandgap of Ge. This permits photoluminescence of excited carriers by both direct and indirect bandgap transitions.…”