High Speed InAl(Ga)N-Barrier HEMTs

Doctoral Dissertation


While the conventional AlGaN-barrier GaN high electron mobility transistors (HEMTs) gradually matured in the past fifteen years, one of the recent research interests is focused on highly scaled structures to achieve high current gain and power gain cut-off frequency fT/fmax for high speed and power amplifying applications. To reach this goal, we must address several critical issues by realizing: 1) low on-resistance (both low ohmic contact resistance and low sheet resistance in the access region), 2) sub-100 nm gate length, 3) minimal gate-drain depletion extension, 4) favorable carrier confinement in the channel with thin top barrier thus high transconductance, 5) sufficient passivation of surface states and traps to suppress the current collapse and frequency dispersion, 6) small parasitic capacitance and gate resistance, and 7) reasonably high breakdown voltage.
In this work, InAlGaN/AlN-barrier HEMTs have been developed for the first time at the University of Notre Dame due to its inherent scalability: thin barriers (1-10 nm, i.e. EOT ~0.5-5 nm) and attractive 2DEG properties (ns > 1 x 10^13 cm-2, mobility> 1000 cm2/V.s). Based on the successful development of ohmic contacts and novel dielectric-free passivation, record performance devices are demonstrated, e.g. fT of 220 GHz with a 66-nm-long trapezoidal gate and fT/fmax of 230/300 GHz with a 40-nm-long T-gate. In this dissertation, advanced epitaxial designs have been investigated in order to obtain excellent transport properties, good scalability, and improved electron confinement for high speed electronics. The process developments have been summarized, including mesa isolation, ohmic contact formation, and T-gate fabrication. The device passivation mechanism with both dielectric films and dielectric-free plasma treatments have been intensively studied and compared, based on which an effective passivation solution for devices with alloyed and non-alloyed ohmic contacts has been proposed: plasma-assisted thin dielectric passivation.


Attribute NameValues
  • etd-04182013-162305

Author Ronghua Wang
Advisor Huili Grace Xing
Contributor Huili Grace Xing, Committee Chair
Contributor Gregory Snider, Committee Member
Contributor Debdeep Jena, Committee Member
Contributor Lei Liu, Committee Member
Contributor Patrick Fay, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Electrical Engineering
Degree Name PhD
Defense Date
  • 2013-04-09

Submission Date 2013-04-18
  • United States of America

  • HFET

  • GaN

  • HEMT

  • passivation

  • InAlN

  • AlInN

  • quaternary

  • AlInGaN

  • barrier height

  • high speed

  • ternary

  • InAlGaN

  • oxidation

  • University of Notre Dame

  • English

Record Visibility Public
Content License
  • All rights reserved

Departments and Units


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