Relationships of the Chemical and Electrical Interfacial Properties of Germanium ‐ SiO2 Systems

Germanium‐silicon dioxide structures were prepared by depositing on cleaned germanium wafers using chemical vapor deposition (CVD) from the silane‐oxygen reaction at 450°C. The structures were then annealed in various gas environments, Ar, , and a  and  forming gas, at 600°C for 2 hr. For samples annealed in forming gas, the interface state density measured by C‐V techniques shows a high density near the band edges (1014/cm2‐eV). For samples annealed in oxygen, it decreases to 1011/cm2‐eV. High surface recombination velocity was observed in the samples annealed in forming gas. The measured results of charge generation and injection indicated charge losses to the interface states but not to oxide traps, whose time constant for trapping is longer than the normal injection time . In order to understand the effects of annealing with different gas environments, profile analyses of the structures were carried out using secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES). For the samples annealed in oxygen, the presence of germanium oxide was identified by observing the low energy Auger spectrum at the interface in comparison with the spectrum obtained for a standard  sample. The profile of the germanium spectrum obtained using SIMS can be used to identify the presence of the oxide because of the enhanced secondary ion yield of the oxide. In the case of the forming gas anneal, the hydrogen appears to diffuse into the interface resulting in a high interface state density. The profile of hydrogen concentration for the structures was also obtained. It is concluded that the increase of the interface state density of a  system due to the forming gas anneal appears to result from dissolved hydrogen diffusing through the . The reduction of interface state density of the structure annealed in oxygen is probably due to the oxidation of germanium and dissolved hydrogen, which reduces the defects originally present in the interface region following the  deposition.

Source:IOPscience

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