|Ph.D Student||Shay Joseph|
|Subject||The Influence of Composition, Microstructure and Thickness|
on the Optical Transparency and Electrical
Conductivity of Thin InxOy Films
|Department||Department of Materials Science and Engineering||Supervisor||Professor Berger Shlomo|
|Full Thesis text|
Indium oxide and Sn doped-indium oxide are the most abundant transparent conductive oxides with visible transparency of over 90% and low sheet resistivity of 10-20Ω/□. However, in the infrared there is currently no satisfactory transparent conductor with the desired levels of optical transparency and electrical conductivity. In an effort to achieve both high infrared transparency and electrical conductivity, InxOy films were deposited on single crystal Si(111) wafers via DC magnetron sputtering at different oxygen flow rates and temperatures. According to SIMS and RBS results, decreasing the oxygen flow, results in films with larger stoichiometric deviation and increased oxygen deficiency. Microstructure analysis based on TEM, XRD and EELS reveals two phases in the stoichiometric films: a crystalline In2O3 phase having the Bixbyite crystallographic structure and amorphous In2O3 phase. In the case of non-stoichiometric films, three phases were found: metallic indium particles, amorphous and crystalline InxOy. The metallic indium particles, 5-30nm in size, are evenly dispersed in the film and occupy less than 1% of its volume. The grain sizes in the crystalline In2O3 phase are 10-100nm. It is claimed that the composition deviation from stoichiometry occurs mostly in the amorphous phase.
From AC electrical measurements it was determined that electrical conductance of stoichiometric InxOy films is governed by the hopping conduction mechanism via energy states located in the band gap. The electrical conductance of the InxOy films having non-stoichiometric compositions was found to be governed by the free band conduction mechanism. For stoichiometric films, the activation energy for electrical conduction was 0.5eV while in the case of the non-stoichiometric films, it was one order of magnitude smaller.
The dielectric function of the films was determined by applying the Drude-Lorentz model to spectroscopic ellipsometric measurements. In the visible range, the major source for optical transmission loss is interband absorption, which was modeled by the Lorentz model. In the infrared range, optical absorption was measured and attributed to the presence of free charge carriers according to the Drude model. Fitting the model to the optical measurements required a correction factor, which was correlated with the films polarizability.
It was shown that by introducing non-stoichiometry in the form of oxygen deficiency, the electrical conductance can be improved by as much as two orders of magnitude while the infrared transparency decreased by no more than 30% with respect to the stoichiometric In2O3 films. Such films, may be sufficient for advanced infrared applications.