Thermodynamic Approach to Gallium Oxide-Metal Contact Formation and Stability
Abstract
Wide-bandgap power devices are technologically critical for many Naval applications including electronic warfare, RF communications, surveillance, and power control systems. Beta-phase gallium oxide semiconductor has recently drawn attention for its ultra-wide bandgap and ease of bulk substrate fabrication compared to SiC and GaN. To reduce power loss in switches and rectifiers, parasitic contact resistance must be minimized. The best ohmic contacts demonstrated to date use titanium thin films in contact with gallium oxide. However from calculation of reaction Gibbs free energies, titanium is predicted to have an thermodynamically unstable interface with gallium oxide, leading to formation of insulating titanium oxides. This may lead to poor device reliability under typical operating conditions. The objectives of this project are: (1) to assess gallium oxide contact reliability to electrical, temperature and illumination stress; (2) to identify new, thermodynamically stable electrode materials through comprehensive modelling and experiments; and (3) to investigate fundamental charge transport mechanisms of metalgallium oxide junctions. To achieve these goals, this project will use comprehensive thermodynamic modeling of metalgallium oxide ternary phase diagrams to predict interlayer formation at metal-gallium oxide interfaces, and thereby down-select stable contact materials for both ohmic and rectifying junctions. This predictive work will be tightly coupled with careful experimental validation using electron-beam analysis to observe in situ oxidation/reduction and microstructure evolution at the interface during annealing. In addition to investigation of elemental metal electrodes, this project will explore use of precisely engineered metal/metal-oxide bilayers to tailor in situ reactions and thus ensure low interface state densities. For promising contact technologies, the contact stability and fundamental charge transport mechanisms will be extensively studied under biastemperature- illumination stress. Finally, this project will investigate the roles of impurities such as dopants or surface cleaning byproducts in determining the thermodynamic and kinetically favorable reaction pathways. This project will make significant fundamental contributions to the understanding of metal junctions with oxides that can subsequently be applied to a broad array of materials systems beyond gallium oxide, including strongly correlated oxides and superconductors. In addition, the insights gained by exploration of oxidation/reduction pathways for metal-gallium oxide contacts can be extended to identify appropriate dielectrics for insulting gates and surface passivation. Furthermore, the technical capabilities developed in this project will directly feed into ongoing gallium oxide epitaxy and device work at ONR and other DoD units
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 03, 2017
- Source ID
- N000141712998
Entities
People
- Becky Peterson
Organizations
- Board of Regents of the University of Michigan
- Office of Naval Research
- United States Navy