Thermal stability study of n-type and p-type ohmic contacts simultaneously formed on 4H-SiC

Abstract

In this paper, Pt/TaSi2/Ni/Ti/Ni/SiC and Pt/Ti/SiC simultaneous ohmic contacts to n-type and p-type 4H-SiC are studied. The thermal stability and electrical characteristics of the ohmic contacts are investigated and compared after being aged at 500 °C for 300 h in air. The n- and p-type Pt/Ti/SiC ohmic contact failed after 100 h and after 200 h, respectively. While the Pt/TaSi2/Ni/Ti/Ni/SiC samples exhibits a good thermal stability and high temperature electrical characteristics, with a relatively small increase of the specific contact resistance (SCR) in the initial 50 h and then remains stable in the rest of the thermal aging duration. SEM analysis reveals that the surface morphologies of Pt/TaSi2/Ni/Ti/Ni/SiC samples keep smooth and stable during the aging process. According to AES analysis, the main reason of electrical characteristics degradation is the oxidation on the metal/4H-SiC interface during the aging process. Also, at the expense of the TaSi2 layer oxidization, the diffusion rate of oxygen atoms towards the SiC are slowed down, and therefore, the metal/4H-SiC interface quality was not affected by oxidation problems and extending the life of ohmic contact in air at 500 °C. Experimental results indicate that the Pt/TaSi2/Ni/Ti/Ni/SiC simultaneous ohmic contacts to both n- and p-type SiC are promising to be used for high temperature and harsh environment SiC-based devices.