Enhancement-mode, high Al-content HEMTs using epitaxial gate oxides

Peter T.Dickens1, Brianna Klein1, Erica Douglass1, Andrew Armstrong1, Andrew Allerman1, Alber Baca1, Michael Brumbach1, Rebecca Chow1, John F. Ihlefeld2, Elizabeth A. Paisley1

  1. Sandia National Laboratories
  2. Department of Materials Science and Engineering, University of Virginia

The development of ultra-wide-bandgap (UWBG) transistors for next generation power electronics is promising owing to their higher breakdown field, thermal conductivity, and saturated electron velocity over traditional silicon insulated gate bipolar transistors. Currently however, the improvement of UWBG transistors is sometimes limited by non-ideal gate performance leading to normally-on operation, high leakage currents, and frequency dispersion. Gate oxide introduction may improve the performance, but many oxides are insufficient for UWBG transistors due to low conduction band offsets and/or poor chemical and structural interface quality. In this work, we will demonstrate that MgO gate insulators are promising gate insulator candidates for high Al-content AlGaN transistors. We have previously shown that MgO provides a sufficient band offset to 85% AlGaN, a high dielectric constant, and epitaxial, chemically abrupt interfaces with AlGaN. In this presentation, we will show our recent data demonstrating that 3 nm MgO provides enhancement-mode transistor performance on 85% Al-content AlGaN by utilizing a fluorine interface treatment prior to oxide growth. Channel currents of 17 mA/mm at +6 V gate bias were achieved with a +0.5 V threshold voltage. We will show the transistor device performance for MgO gated devices compared to normally depletion mode Schottky gated devices on similar device architecture.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.