Low resistivity ohmic contacts on 4H-silicon carbide for high power and high temperature device applications

Abstract

We investigated titanium based ohmic contacts using co-evaporated epitaxial titanium carbide (TiC) on highly doped n +- and p +-type epilayers as well as Al ion implanted layers for high power and high temperature device application. Epitaxially grown TiC ohmic contacts on epilayers as well as Al implanted layers of 4H-SiC were formed by UHV co-evaporation with Ti and C 60 at low substrate temperature. The specific contact resistance ( ρ C) was as low as 5×10 −6, 2×10 −5, and 2×10 −5 Ωcm 2 for TiC contacts on n +, on p + epilayer, and on Al implanted layer, respectively, using a linear TLM measurement. In addition to TiC, we also investigated TiW (weight ratio 30:70) ohmic contacts to p- and n-type 4H-SiC for the purpose of long-term reliability tests at high temperature. The average ρ C of sputtered TiW contacts was 4×10 −5 for p + and n + epilayer. We also found that an evaporated top layer (Au or Pt) helps to protect from degradation of the contacts under long-term reliability tests with temperatures of up to 600°C in a vacuum chamber.