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Keywords:

  • GaN;
  • AlInGaN;
  • InAlGaN;
  • quaternary;
  • enhancement mode;
  • ICP;
  • Al2O3;
  • AlOx;
  • alumnium oxide

Abstract

Enhancement mode GaN-based devices can be realised i.a. by gate recessing or the utilisation of a thin barrier. Yet, as this concept bases upon an increase in barrier capacitance, the application of a gate dielectric causing a capacitance reduction remains as a critical issue. A charge-free dielectric would shift the threshold voltage to negative values, eventually forming a depletion mode device. However, with an appropriate charge-containing dielectric, the same threshold voltage as for an HFET could be maintained. Here, a metal stack consisting of Al and Ti on top of a quaternary In0.11Al0.72Ga0.17N barrier was plasma-oxidised and is shown to form insulated-gate devices with almost the same threshold voltage as their Schottky gate counterparts. The effects on the threshold voltage are discussed. It is shown that the transconductance improves by more than 80%, record drain current of 860 mA/mm is achieved and the dynamic behaviour dramatically improves. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)