Innovation and Partnerships Office

Stable and Highly Conductive Transparent Semiconductors IB-2957

APPLICATIONS OF TECHNOLOGY:

  • Transparent thin film transistors (TFTs)
  • Photovoltaics
  • Resistive oxide memory
  • Photocatalysis and catalysis
  • Chemical sensors

ADVANTAGES:

  • Transparent
  • Stable in an electric field
  • High electron mobility

ABSTRACT:

Scientists at Berkeley Lab have developed a method for inserting halogens into transition metal oxides (TMOs) to generate chemically stable, highly conductive semiconductor materials. These materials would be useful in charge-based devices, such as oxide-based thin film transistors (TFTs) used for fast graphics on transparent and/or flexible displays.

The Berkeley Lab method provides n-type doping to control charge-carrier concentration without decreasing the band gap or reducing the oxygen stoichiometry. As a result, the materials remain stable when placed in an electrical field. In addition, they are produced by dry processing, as is desirable in fabricating charge-based devices.

The scientists created films of fluorine-doped TiO2 by sputtering with an inert gas containing trace amounts of a fluorine precursor. The fluorine insertion led to at least a 40X increase in the conductivity of stoichiometric TiO2 and a 3X increase in the rectification factor of TiO2 on p-type silicon. These effects greatly increase the utility of the material for charge transport / transfer applications in displays, photovoltaics, photocatalysts, catalysts, and chemical sensors.

Controlling the oxygen stoichiometry in TMO semiconductors is an established way to influence charge transport properties, but the chemical instability of oxygen vacancies, especially under an electric field, dramatically limit the lifetime of oxide-based TFT displays because the TFTs become metallic within hours of use due to migration of oxygen vacancies. The Berkeley Lab materials overcome these limitations to provide stable, transparent semiconductors with high conductivity.

DEVELOPMENT STAGE: Prototype: material fabricated and tested.

STATUS: Issued U. S. Patent #9,312,342. Available for licensing or collaborative research.

FOR MORE INFORMATION:

Seo H., L.R. Baker, A. Hervier, J. Kim, J.L. Whitten, G.A. Somorjai. “Generation of highly n-type titanium oxide using plasma fluorine insertion,” Nano Letters 11: 751-756 (2011).

REFERENCE NUMBER: IB-2957