Ohmic & Gate Contacts for High Electron Mobility Transistors (HEMTs)


Ohmic contact degradation and gate-sinking are two major degradation mechanisms that cause semiconductor devices, such as high electron mobility transistors, or HEMTs, to fail. In general, the rapid diffusion of contact metals into the indium phosphide substrates has restricted processing temperatures to 300C and reliable operating temperatures have been limited to 200C to 250C. This set of technologies embodies two similar methods for improving reliability and performance of contacts in indium phosphide-based semiconductors. Both alleviate the diffusion of metals into the semiconductor substrate, and the resulting impairment of device performance, by changing the composition of the metal contacts. For the first time, enhancement mode high electron mobility transistors (e-HEMTs) are practical in these material systems.


By substituting a new metallization scheme in ohmic contacts, and an iridium-based metallization for gate contacts, processing can take place at temperatures greater than 400C, offering a processing temperature window 100C to 150C wider than was available previously. Diffusion of the metal into the substrate is reduced, thereby increasing reliability and operating lifetime. In addition, with the increased Schottky barrier height offered by the use of the new gate metallization, a true reliable indium phosphide enhancement mode HEMT, or e-HEMT, is now possible. An e-HEMT draws no power in its "off" state, a significant benefit in mobile communications applications.


  • Wireless communications
  • Satellite communications
  • Defense applications
  • High-frequency devices


  • Higher temperature annealing
  • Reduced diffusion of contact metal into substrate
  • Higher reliability
  • Higher temperature operation possible
  • Enables true enhancement-mode high electron mobility transistors