A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs

Yen Ku Lin, Johan Bergsten, Hector Leong, Anna Malmros, Jr Tai Chen, Ding Yuan Chen, Olof Kordina, Herbert Zirath, Edward Yi Chang*, Niklas Rorsman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Ω mm after annealing at 575 °C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.

Original languageEnglish
Article number095019
JournalSemiconductor Science and Technology
Volume33
Issue number9
DOIs
StatePublished - 21 Aug 2018

Keywords

  • contact resistance
  • GaN
  • gold-free
  • HEMT
  • ohmic recess
  • sidewall contact

Fingerprint Dive into the research topics of 'A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs'. Together they form a unique fingerprint.

Cite this