Source resistance reduction of AlGaN-GaN HFETs with novel superlattice cap layer

Tomohiro Murata*, Masahiro Hikita, Yutaka Hirose, Yasuhiro Uemoto, Kaoru Inoue, Tsuyoshi Tanaka, Daisuke Ueda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


We have developed a novel AlGaN-GaN heterojunction field effect transistor (HFET) with an ultralow source resistance by employing the novel superlattice (SL) cap structure. The particular advantage of the SL cap, i.e., the existence of multiple layers of the polarization-induced two-dimensional electron gas (2DEG) with high mobility and high concentration at each AlGaN-GaN interface, is fully exploited for lowering the lateral resistance and the potential barrier at the interface of the SL cap and the HFET barrier layer. By designing the AlGaN-GaN thickness ratio, we have established a method to obtain the optimized SL structure and have achieved an extremely low source resistance of 0.4 Ω · mm which is lower not only than HFETs with the conventional structure but also than those with the n-GaN cap structure. The SL cap HFET fabricated on a sapphire substrate exhibited excellent dc and RF performance, i.e., maximum transconductance of over 400 mS/mm, maximum drain current of 1.2 A/mm, a cutoff frequency of 60 GHz, a maximum frequency of oscillation of 140 GHz, and a very low noise figure minimum of 0.7 dB at 12 GHz.

Original languageEnglish
Pages (from-to)1042-1047
Number of pages6
JournalIEEE Transactions on Electron Devices
Issue number6
StatePublished - 1 Jun 2005


  • AlGaN-GaN heterojunction field effect transistors (HFETs)
  • Noise figure
  • Polarization charge
  • Sapphire substrate
  • Source resistance
  • Superlattice cap
  • Two-dimensional electron gas (2DEG)

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