DESIGN OF SHALLOW AND THERMALLY STABLE CONTACTS ON ANTIMONIDE-BASED SEMICONDUCTORS

Open Access
Author:
Wang, Hsiao-an Sammy
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
September 28, 2004
Committee Members:
  • Suzanne E Mohney, Committee Chair
  • Mark William Horn, Committee Member
  • Theresa Stellwag Mayer, Committee Member
  • Joan Marie Redwing, Committee Member
  • James Patrick Runt, Committee Member
Keywords:
  • metal/semiconductor contact
  • ohmic contact
  • Schottky barrier height
  • gate metallization
  • shallow reaction
  • thermal stability
  • aging
  • wet processing
  • surface passivation
  • antimonide based compound semiconductors
  • InGaSb
  • InAs
  • AlGaAsSb
  • HBT
  • HEMT
  • I-V characteristics
  • cross-sectional TEM
Abstract:
This dissertation addresses the development of shallow and thermally stable metallizations for Sb-based compound semiconductors for high speed, low power electronic devices. The factors that influence the contact resistance, thermal stability, and shallowness of the ohmic contacts to p-InGaSb were investigated. These contacts are important for the base of a 6.2 Å heterojunction bipolar transistor. A non-alloyed low resistance Pd/W/Au (2/50/145 nm) ohmic contact prepared using an (NH4)2S rinse treatment was developed with a specific contact resistance of 5.9 x 10^-7 Ohm cm^2. Tungsten serves as a diffusion barrier. Gold lowers the metal sheet resistance, which we have found both experimentally and through modeling to influence of contact resistance measurements, and palladium is used to make intimate contact at the metal/semiconductor interface. It was observed by cross-sectional transmission electron microscopy that the (NH4)2S rinse treatment effectively minimizes the thickness of any residual dielectric layer on the semiconductor, leading to a reduction in the specific contact resistance. In addition, the specific contact resistances of various metal/W/Au (2/50/145 nm) contacts were compared, and the (NH4)2S rinse is found to partially relieve Fermi level pinning at the contact/p-InGaSb interface. Cross-sectional transmission electron microscopy reveals that the Pt/W/Au contacts have better thermal stability than Pd/W/Au contacts, with the Pt/W/Au contacts remaining shallow even after they are aged at 250 °C for 3 days. The thermal stability of various gate metallizations on InAs/AlGaAsSb/InAs heterostructures with and without the InAs cap removed was also investigated. These metallizations are important for high electron mobility transistors fabricated from the antimonide based compound semiconductors. The W/Au gate was found to be a good candidate for making stable contacts directly to AlGaAsSb. The Ti/Pt/Au (50/50/100 nm) and Co/Si/Co/Si/Co metallizations are more thermally stable on InAs than other metallizations tested. It was observed by the cross-sectional transmission electron microscopy that a degradation in the current-voltage characteristics is associated with the metal/InAs reactions, and a proposed energy band diagram was used to explain the degradation mechanism.