Ta 2 O 5 films deposited on Si substrates were investigated using transmission Fourier-transform infrared spectroscopy. We found a new absorption peak at 2340 cm−1 that can be characterized as a stretching vibration mode due to Ta=O bonds in the films. This peak appeared following annealing in O2 ambient, but not in N2 ambient. It was located at 2335 cm−1 in amorphous Ta2O5 films and shifted to 2340 cm−1 after crystallization by annealing at over 700 °C. The bonds associated with the peak were homogeneously distributed in the film. We demonstrated that Ta2O5 films can include strong double bonds between Ta and O (Ta=O) in the structure, independent of whether they are crystalline or amorphous.

No abstract

An attempt is made to control the Schottky barrier height (SBH) of Al/GaAs(100) Schottky barrier diodes by inserting an ultrathin Molecular beam epitaxy (MBE) Si interface control layer (Si ICL). A theory for SBH control including an ideal case and a relaxed case is presented based on the disorder-induced gap state (DIGS) model. The Schottky barrier height (SBH) is measured by the X-ray photoelectron spectroscopy (XPS), current-voltage (I-V) and capacitance-voltage (C-V) techniques. Theory and experiment show that the SBH can be varied precisely over a wide range of about 400 meV by the use of pseudomorphic Si ICL with suitable As doping. When the Si ICL is above the critical thickness of 10 Å, SBH control becomes more difficult due to competition between the ionized dopant atoms and the ionized interface states at the Si ICL-GaAs interface.

The Si–O–Si bonds formed at the Ta2O5/Si interface by annealing were investigated by using Fourier transform infrared absorption spectroscopy. The Ta2O5 thin films deposited on Si substrates were annealed in different ambient (H2O, O2, and N2) at temperatures between 500 and 800 °C. When annealing is done in H2O, the interfacial silicon–oxide grows very rapidly, because the oxidation species can easily diffuse through Ta2O5 films, and because the Si–O formation is controlled by the diffusion of H2O in the interfacial layer. When annealing is done in O2, the oxidation species can also easily diffuse through Ta2O5, but not through the interfacial layer. The interfacial layer is formed by a reaction between Ta2O5 and Si even if the annealing ambient does not contain oxidation species, as is the case when annealing is done in N2. We conclude that the Si–O formation during postannealing in O2 and N2 is controlled by the diffusion of the Si from the substrate through the interfacial layer with an activation energy of 0.7 to 0.8 eV, and that new Si–O bonds are formed at the interface between the Ta2O5 and interfacial layer. Oxidation species from the annealing ambient enhance the frequency factor of the reaction, but do not control Si–O formation.

Silicon–oxide layers formed at the tantalum–oxide/silicon interface were investigated by using Fourier transform infrared spectroscopy (FTIR). The samples were annealed in oxygen atmosphere, in nitrogen atmosphere, and in vacuum. It has been found that the formation of the interfacial silicon–oxide layers depends neither on the tantalum–oxide thickness nor on the annealing atmosphere, but on the annealing temperature. The silicon–oxide layer is formed even by annealing in vacuum. It is concluded that the silicon–oxide layer is formed not by a diffusion of the oxygen from the annealing atmosphere, but by a reaction between the tantalum–oxide film and the Si substrate. FTIR analysis and transmission electron microscopy of the interfacial layer show that the silicon–oxide layer has a bonding configuration different from a pure silicon dioxide.