Reduction Of Interface State Density Research Articles

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.

Auger electron spectroscopy of a stable germanium oxide

A stable germanium oxide is formed by depositing a SiO2 film, by chemical vapor deposition (CVD), on a germanium substrate and annealing in oxygen. Auger electron spectra for this stable germanium oxide are presented. The chemical shifts and the new transitions due to oxidation are shown for some major peaks, e.g., for transitions M45N23N23 the energy shifted from 22.5 to 18 eV, and for L1L3M45 from 106 to 101.5 eV. The energy shifts and new transitions in Auger peaks of a thermally oxidized sample are used to establish the presence of germanium oxide in between the SiO2 and Ge due to the oxidation annealings. The profiles of forming gas-annealed and argon-annealed samples are shown to contain very little oxidized Ge. The reduction of interface state density of Ge metal–insulator–semiconductor (MIS) structures when annealed in O is probably due to the oxidation of Ge (and reduction of dissolved hydrogen) which reduces the defects originally present in the interface region following SiO2 deposition.