Robust Electrical Contacts for Sensors and Electronics in Space Flight

Open Access
Author:
Kragh-Buetow, Katherine Cora
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
December 18, 2015
Committee Members:
  • Suzanne E Mohney, Committee Chair
  • Patrick M Lenahan, Committee Member
  • Joan Marie Redwing, Committee Member
  • Earle Richard Ryba, Committee Member
  • Robert S Okojie, Special Member
Keywords:
  • silicon carbide (SiC)
  • indium nitride (InN)
  • polar semiconductors
  • high temperature
  • ohmic contacts
  • tungsten
  • nickel
Abstract:
The continued advancement of silicon-based electronics has transformed people’s lives around the world; however, silicon is not best suited for all devices or applications. Ohmic contacts to silicon carbide (SiC) were studied for high-temperature electronics and sensors, and to indium nitride (InN) for optoelectronic applications. Ohmic contacts to p- and n-type 4H-SiC using alloyed tungsten–nickel (W:Ni) refractory thin films were investigated. Transfer length measurement test structures on p-SiC (NA = 3 × 10^20 cm^−3) epitaxial layers revealed ohmic contacts with specific contact resistances, ρc, of ~10^−6–10^−5 Ωcm^2 after 0.5 h annealing in argon at 1000–1200 °C. Contacts fabricated on n-SiC (ND = 2 × 10^19 cm^−3) by similar methods were shown to have similar ρc values after annealing at 1000–1150 °C. Together, these ohmic contacts demonstrated the lowest comparable ρc values made simultaneously to both conductivity types. Using simultaneous ohmic contacts would reduce the complexity in fabricating SiC devices. The phases formed were characterized using X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray energy dispersive spectroscopy (XEDS) mapping. In samples annealed at 1100 °C+, the contacts exhibited phase segregation with distinct carbide phases at the surface. Samples annealed at 1000 °C displayed relatively homogeneous tungsten–nickel–carbide layers with smooth surfaces and only slightly higher ρc values. The contacts annealed at 1000 °C also demonstrated the most promise after aging, both briefly at 1000 °C and for 100 h at 600 °C in Ar, with only moderate increases in ρc. The influence of polarity on metal–semiconductor interfaces must be understood for optimizing electrical contacts. Metal–InN interfaces were characterized in a side-by-side study on the polar {0001} faces. The Ni films on (0001) and (000-1) InN exhibited different reaction kinetics upon annealing at 400 °C. Structural and chemical analysis using grazing incidence XRD, transmission electron microscopy, and XEDS indicated a sharp interface between the Ni film and the In-face (0001) InN layer. However, the N-face InN reacted with Ni to form a Ni3InNx ternary phase with an anti-perovskite structure. These results suggest the potential for polarity to impact other metal–semiconductor systems as well.