Understanding the thermal stability of Ohmic contacts

The interface between metal and semiconductor can form an Ohmic contact with very low resistance and yield a linear current-voltage curve prescribed by Ohm’s law. However, these contacts can significantly impede the power output of the devices due to degradation caused by prolonged exposure to high temperatures.

To better understand the mechanism of this degradation, Chen et al. devised a feasible and effective method for studying degradation in Ohmic contacts and designed a contact for 4H-SiC that exhibits improved performance at high temperatures.

The authors fabricated an Ohmic contact containing tungsten, nickel, and silicon carbide, which demonstrated high thermal stability. To study the stability of their device, the authors etched the contact at different depths and determined the phase composition of the contacts at each depth by X-ray photoelectron spectroscopy, or XPS – an advantage over traditional methods that only determine the elemental content or overall phase of Ohmic contacts.

Using XPS, the authors found that contact was stable because nickel, tungsten, and silicon atoms were continuously released as time passed. These atoms then react with oxygen in the air to prevent it from diffusing to the interface and making the device more vulnerable to heat.

Author Zhizhan Chen said that the group plans to continue studying Ohmic contacts. “The degradation mechanism of Ohmic contact will further be studied from the perspective of the interface,” he said. “We will also apply a tungsten/nickel/silicon carbide Ohmic contact to silicon carbide devices such as photoconductive semiconductor switches.”

Source: “In-situ XPS spectroscopic study of thermal stability of W/Ni bilayer Ohmic contact to n-type 4H-SiC,” by Meng-meng Gao, Shu-yue Jiang, Duo Cao, and Zhi-zhan Chen, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0002560 .