Ohmic Contacts to P-Type SiC

摘要

Alloys of aluminum (Al) have previously been used as ohmic contacts to p-type SiC, however the characteristics and performance of these contacts is drastically affected by the type and composition of the Al alloy. This work examined alloys of Al and titanium (Ti) as a junction of alloy composition with the goal of determining the composition which would yield the best ohmic contact to p-type SiC as characterized by a low specific contact resistance, a limited reaction between the metal alloy and the SiC, and reproducibility of contact parameters. After examining 4 Al-Ti alloys, it was determined that a 70/30 weight percent alloy composition of Al and Ti produced low resistance, reproducible ohmic contacts with minimal reaction to p-type SiC. It is further noted that a liquid phase of the alloy must be present during the anneal that forms the ohmic contact. Although this work was performed on heavily doped 4H material, previous work done by the authors supports the conclusion that these results will be valid on all polytypes of SiC with a corresponding increase in specific contact resistance as the doping level of the semiconductor decreases.